Electrical safety-manual

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Safety manual for electrical

Safety manual for electrical

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  • 1. WorkplaceSafety and Health Student Manual
  • 2. Ordering InformationTo receive documents or other information about occupational safety andhealth topics, contact the National Institute for Occupational Safety andHealth (NIOSH) at NIOSH—Publications Dissemination 4676 Columbia Parkway Cincinnati, OH 45226–1998 Telephone: 1–800–35–NIOSH (1–800–356–4674) Fax number: 513–533–8573 E-mail: pubstaft@cdc.gov or visit the NIOSH Web site at www.cdc.gov/niosh This document is in the public domain and may be freely copied or reprinted. Disclaimer: Mention of any company or product does not constitute endorsement by NIOSH. DHHS (NIOSH) Publication No. 2002-123
  • 3. Student ManualJanuary 2002
  • 4. Acknowledgments This document was prepared by Thaddeus W. Fowler, Ed.D., and Karen K. Miles, Ph.D., Education and Information Division (EID) of the National Institute for Occupational Safety and Health (NIOSH). Editorial services were provided by John W. Diether. Pauline Elliott provided layout and design. The authors wish to thank John Palassis and Diana Flaherty (NIOSH), Robert Nester (formerly of NIOSH), and participating teachers and students for their contributions to the development of this document.ii
  • 5. ForewordThe National Institute for Occupational Safety and Health (NIOSH) estimatesthat 200,000 young workers under the age of 18 suffer work-related injuries inthe United States each year. Young and new workers have a high risk for work-related injury compared with more experienced workers. Occupational safetyand health training remains a fundamental element of hazard control in the work-place, and there is great potential to reduce these incidents through pre-employ-ment training. Effective pre-employment training should include realistic envi-ronments and hands-on exercises. However, NIOSH recommends that actualemployment in the electrical trades or any of the other construction trades bedelayed until individuals reach the minimum age of 18.This student manual is part of a safety and health curriculum for secondary andpost-secondary electrical trades courses. The manual is designed to engage thelearner in recognizing, evaluating, and controlling hazards associated with elec-trical work. It was developed through extensive research with vocational instruc-tors, and we are grateful for their valuable contributions. Kathleen M. Rest, Ph.D., M.P.A. Acting Director National Institute for Occupational Safety and Health iii
  • 6. Contents PageSection 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Electricity Is Dangerous . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 How Is an Electrical Shock Received? . . . . . . . . . . . . . . . . . . . . . 2 Summary of Section 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Section 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Dangers of Electrical Shock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Summary of Section 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Section 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Burns Caused by Electricity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Electrical Fires . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Summary of Section 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15First Aid Fact Sheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16Section 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18Overview of the Safety Model . . . . . . . . . . . . . . . . . . . . . . . . . . 18 What Must Be Done to Be Safe? . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Summary of Section 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21Section 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22Safety Model Stage 1—Recognizing Hazards . . . . . . . . . . . . . . . . . 22 How Do You Recognize Hazards? . . . . . . . . . . . . . . . . . . . . . . . . 22 Inadequate wiring hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Exposed electrical parts hazards . . . . . . . . . . . . . . . . . . . . . . . 24 Overhead powerline hazards . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Defective insulation hazards . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Improper grounding hazards . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Overload hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Wet conditions hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Additional hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Summary of Section 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33Section 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34Safety Model Stage 2—Evaluating Hazards . . . . . . . . . . . . . . . . . . 34 How Do You Evaluate Your Risk? . . . . . . . . . . . . . . . . . . . . . . . . 34 Summary of Section 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 v
  • 7. Contents (continued) Page Section 7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 Safety Model Stage 3—Controlling Hazards: Safe Work Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 How Do You Control Hazards? . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 How Do You Create a Safe Work Environment? . . . . . . . . . . . . . . 36 Lock out and tag out circuits and equipment . . . . . . . . . . . . . . 37 Lock-out/tag-out checklist . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 Control inadequate wiring hazards . . . . . . . . . . . . . . . . . . . . . 39 Control hazards of fixed wiring . . . . . . . . . . . . . . . . . . . . . . . . 40 Control hazards of flexible wiring . . . . . . . . . . . . . . . . . . . . . . 40 Use flexible wiring properly . . . . . . . . . . . . . . . . . . . . . . . . 40 Use the right extension cord . . . . . . . . . . . . . . . . . . . . . . . . 42 Control hazards of exposed live electrical parts: isolate energized components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Control hazards of exposure to live electrical wires: use proper insulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Control hazards of shocking currents . . . . . . . . . . . . . . . . . . . . 46 Ground circuits and equipment . . . . . . . . . . . . . . . . . . . . . . 46 Use GFCI’s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 Bond components to assure grounding path . . . . . . . . . . . . 49 Control overload current hazards . . . . . . . . . . . . . . . . . . . . . . . 50 Summary of Section 7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 Section 8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 Safety Model Stage 3—Controlling Hazards: Safe Work Practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 How Do You Work Safely? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 Plan your work and plan for safety . . . . . . . . . . . . . . . . . . . . . 55 Ladder safety fact sheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 Avoid wet working conditions and other dangers . . . . . . . . . . . 61 Avoid overhead powerlines . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 Use proper wiring and connectors . . . . . . . . . . . . . . . . . . . . . . 61 Use and maintain tools properly . . . . . . . . . . . . . . . . . . . . . . . 64 Wear correct PPE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 PPE fact sheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 Summary of Section 8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 Glossary of Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 Endnotes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 Index ................................................ 76 Photo and Graphics Credits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77vi
  • 8. Electrical SafetySection 1 Note to the learner—This manual describes the hazards of electrical work and basic approaches to working safely.Electricity Is Dangerous You will learn skills to help you recognize, evaluate, and control electrical hazards.Whenever you work with power tools or on electrical circuits there This information will prepare you for addi-is a risk of electrical hazards, especially electrical shock. Anyone tional safety training such as hands-oncan be exposed to these hazards at home or at work. Workers are exercises and more detailed reviews ofexposed to more hazards because job sites can be cluttered with regulations for electrical work.tools and materials, fast-paced, and open to the weather. Risk is also Your employer, co-workers, and communityhigher at work because many jobs involve electric power tools. will depend on your expertise. Start your career off right by learning safe practices and developing good safety habits. SafetyElectrical trades workers must pay special attention to electrical haz- is a very important part of any job. Do itards because they work on electrical circuits. Coming in contact with right from the start.an electrical voltage can cause current to flow through the body,resulting in electrical shock and burns. Serious injury or even death „ Electrical shock causes injury ormay occur. As a source of energy, electricity is used without much death!thought about the hazards it can cause. Because electricity is a famil-iar part of our lives, it often is not treated with enough caution. As aresult, an average of one worker is electrocuted on the job every dayof every year! Electrocution is the third leading cause of work-related deaths among 16- and 17-year-olds, after motor vehicledeaths and workplace homicide. Electrocution is the cause of12% of all workplace deaths among young workers.1 Electrical work can be deadly if not done safely.Section 1 Page 1
  • 9. ELECTRICITY This manual will present many topics. There are four main types of electrical injuries: electrocution (death due to electrical shock), electrical shock, burns, and falls. The dangers of electricity, electri- cal shock, and the resulting injuries will be discussed. The various electrical hazards will be described. You will learn about the Safety Model, an important tool for recognizing, evaluating, and con- trolling hazards. Important definitions and notes are shown in the margins. Practices that will help keep you safe and free of injury are emphasized. To give you an idea of the hazards caused by electricity, case studies about real-life deaths will be described.„ current—the movement of How Is an Electrical Shock Received? electrical charge„ voltage—a measure of An electrical shock is received when electrical current passes electrical force through the body. Current will pass through the body in a variety of„ circuit—a complete path for the flow situations. Whenever two wires are at different voltages, current will of current pass between them if they are connected. Your body can connect the„ You will receive a shock if you touch two wires at different wires if you touch both of them at the same time. Current will pass voltages at the same time. through your body. Wires carry current. In most household wiring, the black wires and the red wires are at„ ground—a physical electrical con- 120 volts. The white wires are at 0 volts because they are connected nection to the earth to ground. The connection to ground is often through a conducting„ energized (live, “hot”)—similar ground rod driven into the earth. The connection can also be made terms meaning that a voltage is through a buried metal water pipe. If you come in contact with an present that can cause a current, so there is a possibility of getting shockedPage 2 Section 1
  • 10. I S DA N G E RO U S energized black wire—and you are also in contact with the neu- „ conductor—material in which an tral white wire—current will pass through your body. You will electrical current moves easily receive an electrical shock. „ neutral—at ground potential (0 volts) because of a connection to ground Metal electrical boxes should be grounded to prevent shocks. Black and red wires are usually energized, and white wires are usually neutral. If you are in contact with a live wire or any live component of an „ You will receive a shock if energized electrical device—and also in contact with any you touch a live wire and are grounded at the same time. grounded object—you will receive a shock. Plumbing is often grounded. Metal electrical boxes and conduit are grounded. „ When a circuit, electrical component, or equipment is Your risk of receiving a shock is greater if you stand in a puddle of energized, a potential shock hazard is present. water. But you don’t even have to be standing in water to be at risk. Wet clothing, high humidity, and perspiration also increase your chances of being electrocuted. Of course, there is always a chance of electrocution, even in dry conditions. Section 1 Page 3
  • 11. ELECTRICITY You can even receive a shock when you are not in contact with an electrical ground. Contact with both live wires of a 240-volt cable will deliver a shock. (This type of shock can occur because one live wire may be at +120 volts while the other is at -120 volts during an alternating current cycle—a difference of 240 volts.). You can also receive a shock from electrical components that are not grounded properly. Even contact with another person who is receiving an elec- trical shock may cause you to be shocked. 30-year-old male electrical technician was helping a company service representative test the volt- A age-regulating unit on a new rolling mill. While the electrical technician went to get the equipment service manual, the service representative opened the panel cover of the voltage regulator’s con- trol cabinet in preparation to trace the low-voltage wiring in question (the wiring was not color-coded). The service representative climbed onto a nearby cabinet in order to view the wires. The technician returned and began working inside the control cabinet, near exposed energized electrical conductors. The techni- cian tugged at the low-voltage wires while the service representative tried to identify them from above. Suddenly, the representative heard the victim making a gurgling sound and looked down to see the victim shaking as though he were being shocked. Cardiopulmonary resuscitation (CPR) was administered to the victim about 10 minutes later. He was pronounced dead almost 2 hours later as a result of his contact with an energized electrical conductor. To prevent an incident like this, employers should take the following steps: • Establish proper rules and procedures on how to access electrical control cabinets without getting hurt. • Make sure all employees know the importance of de-energizing (shutting off) electrical systems before performing repairs. • Equip voltage-regulating equipment with color-coded wiring. • Train workers in CPR. maintenance man rode 12 feet above the floor on a motorized lift to work on a 277-volt light fixture. A He did not turn off the power supply to the lights. He removed the line fuse from the black wire, which he thought was the “hot” wire. But, because of a mistake in installation, it turned out that the white wire was the “hot” wire, not the black one. The black wire was neutral. He began to strip the white wire using a wire stripper in his right hand. Electricity passed from the “hot” white wire to the stripper, then into his hand and through his body, and then to ground through his left index finger. A co-worker heard a noise and saw the victim lying face-up on the lift. She immediately summoned another worker, who low- ered the platform. CPR was performed, but the maintenance man could not be saved. He was pronounced dead at the scene. You can prevent injuries and deaths by remembering the following points: • If you work on an electrical circuit, test to make sure that the circuit is de-energized (shut off)! • Never attempt to handle any wires or conductors until you are absolutely positive that their electrical supply has been shut off. • Be sure to lock out and tag out circuits so they cannot be re-energized. • Always assume a conductor is dangerous.Page 4 Section 1
  • 12. I S DA N G E RO U S Always test a circuit to make sure it is de-energized before working on it. Summary of Section 1 You will receive an electrical shock if a part of your body completes an electrical circuit by • • • touching a live wire and an electrical ground, or touching a live wire and another wire at a different voltage. Section 1 Page 5
  • 13. DA N G E R S O F E L E Section 2 Dangers of Electrical Shock The severity of injury from electrical shock depends on the amount of electrical current and the length of time the current passes „ ampere (amp)—the unit used to measure current through the body. For example, 1/10 of an ampere (amp) of elec- tricity going through the body for just 2 seconds is enough to cause death. The amount of internal current a person can withstand and still be able to control the muscles of the arm and hand can be less „ milliampere (milliamp or mA)— 1/1,000 of an ampere than 10 milliamperes (milliamps or mA). Currents above 10 mA can paralyze or “freeze” muscles. When this “freezing” happens, a „ shocking current—electrical current person is no longer able to release a tool, wire, or other object. In that passes through a part of the fact, the electrified object may be held even more tightly, resulting body in longer exposure to the shocking current. For this reason, hand- „ You will be hurt more if you can’t held tools that give a shock can be very dangerous. If you can’t let let go of a tool giving a shock. go of the tool, current continues through your body for a longer time, which can lead to respiratory paralysis (the muscles that con- trol breathing cannot move). You stop breathing for a period of „ The longer the shock, the greater time. People have stopped breathing when shocked with currents the injury. from voltages as low as 49 volts. Usually, it takes about 30 mA of current to cause respiratory paralysis. Currents greater than 75 mA cause ventricular fibrillation (very rapid, ineffective heartbeat). This condition will cause death within a few minutes unless a special device called a defibrillator is used to save the victim. Heart paralysis occurs at 4 amps, which means the heart does not pump at all. Tissue is burned with currents greater than 5 amps.2 The table shows what usually happens for a range of currents (lasting one second) at typical household voltages. Longer exposure times increase the danger to the shock victim. For example, a cur- rent of 100 mA applied for 3 seconds is as dangerous as a current of 900 mA applied for a fraction of a second (0.03 seconds). The mus- cle structure of the person also makes a difference. People with less muscle tissue are typically affected at lower current levels. Even low voltages can be extremely dangerous because the degree of injury depends not only on the amount of current but also on the length of time the body is in contact with the circuit.Defibrillator in use. LOW VOLTAGE DOES NOT MEAN LOW HAZARD! Page 6 Section 2
  • 14. CTRICAL SHOCK Effects of Electrical Current* on the Body3 Current Reaction 1 milliamp Just a faint tingle. 5 milliamps Slight shock felt. Disturbing, but not painful. Most people can “let go.” However, strong involuntary movements can cause injuries. 6–25 milliamps (women)† Painful shock. Muscular control is lost. This is the range where “freezing 9–30 milliamps (men) currents” start. It may not be possible to “let go.” 50–150 milliamps Extremely painful shock, respiratory arrest (breathing stops), severe muscle contractions. Flexor muscles may cause holding on; extensor muscles may cause intense pushing away. Death is possible. 1,000–4,300 milliamps Ventricular fibrillation (heart pumping action not rhythmic) occurs. Muscles (1–4.3 amps) contract; nerve damage occurs. Death is likely. 10,000 milliamps Cardiac arrest and severe burns occur. Death is probable. (10 amps) 15,000 milliamps Lowest overcurrent at which a typical fuse or circuit breaker opens a circuit! (15 amps) *Effects are for voltages less than about 600 volts. Higher voltages also cause severe burns. †Differences in muscle and fat content affect the severity of shock. Sometimes high voltages lead to additional injuries. High voltages „ High voltages cause additional can cause violent muscular contractions. You may lose your balance injuries! and fall, which can cause injury or even death if you fall into machinery that can crush you. High voltages can also cause severe burns (as seen on pages 9 and 10). At 600 volts, the current through the body may be as great as 4 amps, causing damage to internal organs such as the heart. High „ Higher voltages can cause larger voltages also produce burns. In addition, internal blood vessels may currents and more severe shocks. clot. Nerves in the area of the contact point may be damaged. Muscle contractions may cause bone fractures from either the con- tractions themselves or from falls. A severe shock can cause much more damage to the body than is „ Some injuries from electrical visible. A person may suffer internal bleeding and destruction of tis- shock cannot be seen. sues, nerves, and muscles. Sometimes the hidden injuries caused by electrical shock result in a delayed death. Shock is often only the beginning of a chain of events. Even if the electrical current is too small to cause injury, your reaction to the shock may cause you to fall, resulting in bruises, broken bones, or even death. The length of time of the shock greatly affects the amount of injury. If the shock is short in duration, it may only be painful. A longer Section 2 Page 7
  • 15. DA N G E R S O F E L shock (lasting a few seconds) could be fatal if the level of current is high enough to cause the heart to go into ventricular fibrillation. This is not much current when you realize that a small power drill uses 30 times as much current as what will kill. At relatively high currents, death is certain if the shock is long enough. However, if the shock is short and the heart has not been damaged, a normal heartbeat may resume if contact with the electrical current is elimi- nated. (This type of recovery is rare.)„ The greater the current, the The amount of current greater the shock! passing through the body also affects the severity of„ Severity of shock depends on an electrical shock. Greater voltage, amperage, and resist- ance. voltages produce greater currents. So, there is greater danger from higher voltages. Resistance hin- ders current. The lower the„ resistance—a materials ability to resistance (or impedance in decrease or stop electrical current AC circuits), the greater the current will be. Dry skin may have a resistance of 100,000 ohms or more. Wet skin may have a resistance of only 1,000 ohms. Wet working conditions or bro-„ ohm—unit of measurement for ken skin will drastically electrical resistance reduce resistance. The low resistance of wet skin Power drills use 30 times as allows current to pass into much current as what will kill. the body more easily and„ Lower resistance causes greater currents. give a greater shock. When more force is applied to the contact point or when the contact area is larger, the resistance is lower, causing stronger shocks. The path of the electrical current through the body affects the severi- ty of the shock. Currents through the heart or nervous system are most dangerous. If you contact a live wire with your head, your nerv- ous system will be damaged. Contacting a live electrical part with one hand—while you are grounded at the other side of your body—„ Currents across the chest are very will cause electrical current to pass across your chest, possibly injur- dangerous. ing your heart and lungs.Page 8 Section 2
  • 16. ECTRICAL SHOCK male service technician arrived at a customer’s house to perform pre-winter maintenance on an oil A furnace. The customer then left the house and returned 90 minutes later. She noticed the service truck was still in the driveway. After 2 more hours, the customer entered the crawl space with a flashlight to look for the technician but could not see him. She then called the owner of the company, who came to the house. He searched the crawl space and found the technician on his stomach, leaning on his elbows in front of the furnace. The assistant county coroner was called and pronounced the technician dead at the scene. The victim had electrical burns on his scalp and right elbow. After the incident, an electrician inspected the site. A toggle switch that supposedly controlled electrical power to the furnace was in the “off” position. The electrician described the wiring as “haphazard and confusing.” Two weeks later, the county electrical inspector performed another inspection. He discovered that incor- rect wiring of the toggle switch allowed power to flow to the furnace even when the switch was in the “off” position. The owner of the company stated that the victim was a very thorough worker. Perhaps the victim performed more maintenance on the furnace than previous technicians, exposing himself to the electrical hazard. This death could have been prevented! • The victim should have tested the circuit to make sure it was de-energized. • Employers should provide workers with appropriate equipment and training. Using safety equipment should be a requirement of the job. In this case, a simple circuit tester may have saved the victim’s life. • Residential wiring should satisfy the National Electrical Code (NEC). Although the NEC is not retroac- tive, all homeowners should make sure their systems are safe. „ NEC—National Electrical Code— a comprehensive listing of practices to protect workers and equipment from electrical hazards such as fire and electrocution Electrical burn on hand and arm. Section 2 Page 9
  • 17. DA N G E R S O F E L There have been cases where an arm or leg is severely burned by high-voltage electrical current to the point of coming off, and the victim is not electrocuted. In these cases, the current passes through only a part of the limb before it goes out of the body and into another conductor. Therefore, the current does not go through the chest area and may not cause death, even though the victim is severely disfig- ured. If the current does go through the chest, the person will almost surely be electrocuted. A large number of serious electrical injuries involve current passing from the hands to the feet. Such a path involves both the heart and lungs. This type of shock is often fatal. Arm with third degree burn from high-voltage line.Page 10 Section 2
  • 18. ECTRICAL SHOCK Summary of Section 2 The danger from electrical shock depends on • • • the amount of the shocking current through the body, the duration of the shocking current through the body, and the path of the shocking current through the body. Section 2 Page 11
  • 19. B U R N S C AU S E D Section 3 Burns Caused by Electricity The most common shock-related, nonfatal injury is a burn. Burns„ Electrical shocks cause burns. caused by electricity may be of three types: electrical burns, arc burns, and thermal contact burns. Electrical burns can result when a person touches electrical wiring or equipment that is used or main- tained improperly. Typically, such burns occur on the hands. Electrical burns are one of the most serious injuries you can receive. They need to be given immediate attention. Additionally, clothing may catch fire and a„ arc-blast—explosive release of molten material from equipment caused by thermal burn may result from the high-amperage arcs heat of the fire. Contact electrical burns. The knee on the left was energized, Arc-blasts occur when powerful, and the knee on the right was high-amperage currents arc grounded. through the air. Arcing is the„ arcing—the luminous electrical dis- charge (bright, electrical sparking) luminous electrical discharge that occurs when high voltages exist through the air that occurs when high across a gap between conductors and current travels through the air. voltages exist across a gap between This situation is often caused by equipment failure due to abuse or conductors fatigue. Temperatures as high as 35,000°F have been reached in arc-blasts. There are three primary hazards associated with an arc-blast. (1) Arcing gives off thermal radiation (heat) and intense light, which can cause burns. Several factors affect the degree of injury, includ- ing skin color, area of skin exposed, and type of clothing worn. Proper clothing, work distances, and overcurrent protection can reduce the risk of such a burn. (2) A high-voltage arc can produce a considerable pressure wave blast. A person 2 feet away from a 25,000-amp arc feels a force of about 480 pounds on the front of the body. In addition, such an explosion can cause serious ear damage and memory loss due to concussion. Sometimes the pressure wave throws the victim away from the arc-blast. While this may reduce further exposure to thePage 12 Section 3
  • 20. BY ELECTRICITY thermal energy, serious physical injury may result. The pressure wave can propel large objects over great distances. In some cases, the pressure wave has enough force to snap off the heads of steel bolts and knock over walls. (3) A high-voltage arc can also cause many of the copper and alu- minum components in electrical equipment to melt. These droplets of molten metal can be blasted great distances by the pressure wave. Although these droplets harden rapidly, they can still be hot enough to cause serious burns or cause ordinary clothing to catch fire, even if you are 10 feet or more away. ive technicians were performing preventive maintenance on the electrical system of a railroad main- F tenance facility. One of the technicians was assigned to clean the lower compartment of an electri- cal cabinet using cleaning fluid in an aerosol can. But, he began to clean the upper compartment as well. The upper compartment was filled with live circuitry. When the clean- ing spray contacted the live circuitry, a conductive path for the current was created. The current passed through the stream of fluid, into the technician’s arm, and across his chest. The current caused a loud explosion. Co-workers found the victim with his clothes on fire. One worker put out the fire with an extinguisher, and another pulled the vic- tim away from the compartment with a plastic vacuum cleaner hose. The paramedics responded in 5 minutes. Although the victim sur- vived the shock, he died 24 hours later of burns. This death could have been prevented if the following precautions had been taken: • Before doing any electrical work, de-energize all circuits and equipment, perform lock-out/tag-out, and test circuits and equipment to make sure they are de-energized. • The company should have trained the workers to perform their jobs safely. • Proper personal protective equipment (PPE) should always be used. • Never use aerosol spray cans around high-voltage equipment. Section 3 Page 13
  • 21. B U R N S C AU S E D Electrical Fires Electricity is one of the most common causes of fires and thermal burns in homes and workplaces. Defective or misused electrical equipment is a major cause of electrical fires. If there is a small electrical fire, be sure to use only a Class C or multi- purpose (ABC) fire extinguisher, or you might make the problem worse. All fire extinguishers are marked with letter(s) that tell you the kinds of fires they can put out. Some extinguishers contain symbols, too. The letters and symbols are explained below (including suggestions on how to remember them). A (think: Ashes) = paper, wood, etc. B (think: Barrel) = flammable liquids C (think: Circuits) = electrical fires Here are a couple of fire extinguishers at a worksite. Can you tell what types of fires they will put out? This extinguisher can only This extinguisher can only be used on Class B and be used on Class A and Class C fires. Class C fires. Learn how to use fire However, do not try to put out fires unless you have received extinguishers at work. proper training. If you are not trained, the best thing you can do is evacuate the area and call for help.14 Section 3
  • 22. BY ELECTRICITY Thermal burns may result if an explosion occurs when electricity ignites an explosive mixture of material in the air. This ignition can result from the buildup of combustible vapors, gasses, or dusts. Occupational Safety and Health Administration (OSHA) standards, „ OSHA—Occupational Safety and the NEC, and other safety standards give precise safety requirements Health Administration—the Federal agency in the U.S. Department of for the operation of electrical systems and equipment in such dan- Labor that establishes and enforces gerous areas. Ignition can also be caused by overheated conductors workplace safety and health or equipment, or by normal arcing at switch contacts or in circuit regulations breakers. Summary of Section 3 Burns are the most common injury caused by electricity. The three types of burns are • • • electrical burns, arc burns, and thermal contact burns. Section 3 Page 15
  • 23. First Aid Fact Sheet What Should I Do If a Co-Worker Is Shocked or Burned by Electricity? the electrical current if the victim is still in contactShut off with the energized circuit. While you do this, have someone else call for help. If you cannot get to theswitchgear quickly, pry the victim from the circuit with something that does notconduct electricity such as dry wood. Do not touch the victim yourself if he orshe is still in contact with an electrical circuit! You do not want to be a victim, too!Do not leave the victim unless there is absolutely no other option. You should staywith the victim while Emergency Medical Services (EMS) is contacted. The callershould come back to you afterwards to verify that the call was made. If the victim isnot breathing, does not have a heartbeat, or is badly injured, quick response by ateam of emergency medical technicians (EMT’s) or paramedics gives the best chancefor survival. Learn first aidPage 16
  • 24. Once you know that electrical current is no longer flowing through the victim, call out to the victim to see if he or she is conscious (awake). If the victim is conscious, tell the victim not to move. It is possible for a shock victim to be seriously injured but not realize it. Quickly examine the victim for signs of major bleeding. If there is a lot of bleeding, place a cloth (such as a handkerchief or bandanna) over the wound and apply pressure. If the wound is in an arm or leg and keeps bleed- ing a lot, gently elevate the injured area while keeping pressure on the wound. Keep the victim warm and talk to him or her until help arrives. If the victim is unconscious, check for signs of breathing. While you do this, move the victim as little as possible. If the victim is not breathing, someone trained in CPR should begin artificial breathing, then check to see if the victim has a pulse. Quick action is essential! To be effective, CPR must be performed within 4 minutes of the shock. If you are not trained in CPR or first aid, now is the time to get trained—before you find yourself in this situation! Ask your instructor or supervisor how you can become certified in CPR. You also need to know the location of (1) electricity shut-offs (“kill switches”), (2) first-aid sup- plies, and (3) a telephone so you can find them quickly in an emergency.and CPR now! Page 17
  • 25. OV E RV I E W O F T H E Section 4: Overview of the Safety Model What Must Be Done to Be Safe?„ Use the safety model to recognize, Use the three-stage safety model: recognize, evaluate, and control evaluate, and control hazards. hazards. To be safe, you must think about your job and plan for hazards. To avoid injury or death, you must understand and recognize hazards. You need to evaluate the situation you are in and assess your risks. You need to control haz- ards by creating a safe work environment, by using safe work practices, and by report- ing hazards to a supervisor or teacher. If you do not recognize, evalu- ate, and control hazards, you may be injured or killed by the electricity itself, electrical fires, or falls. If you use the Report hazards to your supervisor safety model to recognize, or teacher. evaluate, and control hazards, you are much safer.„ Identify electrical hazards. (1) Recognize hazards The first part of the safety model is recognizing the hazards around you. Only then can you avoid or control the hazards. It is best to discuss and plan hazard recognition tasks with your co-workers.„ Don’t listen to reckless, Sometimes we take risks ourselves, but when we are responsible for dangerous people. others, we are more careful. Sometimes others see hazards that we overlook. Of course, it is possible to be talked out of our concernsPage 18 Section 4
  • 26. SAFETY MODEL by someone who is reckless or dangerous. Don’t take a chance. Careful planning of safety procedures reduces the risk of injury. Decisions to lock out and tag out circuits and equipment need to be made during this part of the safety model. Plans for action must be made now. OSHA regulations, the NEC, and the National Electrical Safety Code (NESC) provide a wide range of safety information. Although these sources may be difficult to read and understand at first, with practice they can become very useful tools to help you recognize unsafe conditions and practices. Knowledge of OSHA standards is an important part of training for electrical apprentices. See the Appendix for a list of relevant standards. Always lock out and tag out circuits. (2) Evaluate hazards When evaluating hazards, it is best to identify all possible hazards „ Evaluate your risk. first, then evaluate the risk of injury from each hazard. Do not assume the risk is low until you evaluate the hazard. It is dangerous to overlook hazards. Job sites are especially dangerous because they are always changing. Many people are working at different tasks. Job sites are frequently exposed to bad weather. A reasonable place to work on a bright, sunny day might be very hazardous in the rain. The risks in your work environment need to be evaluated all the time. Then, whatever hazards are present need to be controlled. (3) Control hazards Once electrical hazards have been recognized and evaluated, they „ Take steps to control hazards: must be controlled. You control electrical hazards in two main ways: Create a safe workplace. Work safely. (1) create a safe work environment and (2) use safe work practices. Controlling electrical hazards (as well as other hazards) reduces the risk of injury or death. Section 4 Page 19
  • 27. OV E RV I E W O F T H EUse the safety model to recognize, evaluate, and control workplace hazards like those inthis picture.Page 20 Section 4
  • 28. SAFETY MODEL Summary of Section 4 The three stages of the safety model are • • • Stage 1— Recognize hazards Stage 2— Evaluate hazards Stage 3— Control hazards Section 4 Page 21
  • 29. S A F E T Y M O D E L S TA G E 1 Section 5 Safety Model Stage 1— Recognizing Hazards How Do You Recognize Hazards? The first step toward protecting yourself is recognizing the many hazards you face on the job. To do this, you must know which situa- tions can place you in danger. Knowing where to look helps you to recognize hazards. u Inadequate wiring is dangerous. u Exposed electrical parts are dangerous.„ Workers face many hazards on the job. u Overhead powerlines are dangerous. u Wires with bad insulation can give you a shock. u Electrical systems and tools that are not grounded or double-insu- lated are dangerous. u Overloaded circuits are dangerous. u Damaged power tools and equipment are electrical hazards. u Using the wrong PPE is dangerous. u Using the wrong tool is dangerous. u Some on-site chemicals are harmful. u Defective ladders and scaffolding are dangerous. u Ladders that conduct electricity are dangerous. u Electrical hazards can be made worse if the worker, location, or equipment is wet.Page 22 Section 5
  • 30. —RECOGNIZING HAZARDS Worker was electrocuted while removing energized fish tape. n electrician was removing a metal fish tape from a hole at the base of a metal light pole. (A A fish tape is used to pull wire through a conduit run.) The fish tape became energized, electro- cuting him. As a result of its inspection, OSHA issued a citation for three serious violations of the agency’s construction standards. If the following OSHA requirements had been followed, this death could have been prevented. • De-energize all circuits before beginning work. • Always lock out and tag out de-energized equipment. • Companies must train workers to recognize and avoid unsafe conditions associ- ated with their work. Fish tape. Section 5 Page 23
  • 31. S A F E T Y M O D E L S TA G E 1 Inadequate wiring hazards„ wire gauge—wire size or diameter An electrical hazard exists when the wire is too small a gauge for the (technically, the cross-sectional area) current it will carry. Normally, the circuit breaker in a circuit is matched to the wire size. However, in older wiring, branch lines to permanent ceiling light fixtures could be wired with a smaller gauge than the supply cable. Let’s say a light fixture is replaced with another„ ampacity—the maximum amount device that uses more current. The current capacity (ampacity) of the of current a wire can carry safely branch wire could be exceeded. When a wire is too small for the cur- without overheating rent it is supposed to carry, the wire will heat up. The heated wire„ Overloaded wires get hot! could cause a fire. When you use an extension cord, the size of the wire you are plac- ing into the circuit may be too small for the equipment. The circuit breaker could be the right size for the circuit but not right for the smaller-gauge extension cord. A tool plugged into the extension cord may use more current than the cord can handle without tripping the circuit breaker. The wire will overheat and could cause a fire. The kind of metal used as a conductor can cause an electrical hazard. Special care needs to be taken with aluminum wire. Since it is more brittle than copper, aluminum wire can crack and break more easily. Connections with aluminum wire can become loose and oxidize if not made properly, creating heat or arcing. You„ Incorrect wiring practices can need to recognize that inade- cause fires! quate wiring is a hazard. Exposed electrical parts hazards Electrical hazards exist when wires or other electrical parts are exposed. Wires and parts can be exposed if a cover is removed from a wiring or breaker box. The overhead wires coming into a home may be exposed. Electrical„ If you touch live electrical parts, This hand-held sander has you will be shocked. exposed wires and should not be used.Page 24 Section 5
  • 32. —RECOGNIZING HAZARDS terminals in motors, appliances, and electronic equipment may be exposed. Older equipment may have exposed electrical parts. If you contact exposed live electrical parts, you will be shocked. You need to recognize that an exposed electrical component is a hazard. Overhead powerline hazards „ Overhead powerlines kill many workers! Most people do not realize that overhead powerlines are usually not insulated. More than half of all electrocutions are caused by direct worker contact with energized powerlines. Powerline workers must be especially aware of the dangers of overhead lines. In the past, 80% of all lineman deaths were caused by contacting a live wire with a bare hand. Due to such incidents, all linemen now wear spe- cial rubber gloves that protect them up to 34,500 volts. Today, most electrocutions involving overhead powerlines are caused by failure to maintain proper work distances. Watch out for exposed electrical wires around Electrical line workers need special training electronic equipment. and equipment to work safely. Section 5 Page 25
  • 33. S A F E T Y M O D E L S TA G E 1 Shocks and electrocutions occur where physical barriers are not in place to prevent contact with the wires. When dump trucks, cranes, work platforms, or other conductive materials (such as pipes and ladders) contact overhead wires, the equipment operator or other workers can be killed. If you do not maintain required clearance distances from powerlines, you can be shocked and killed. (The minimum distance for voltages up to 50kV is 10 feet. For voltages over 50kV, the minimum distance is 10 feet plus 4 inches for every 10 kV over 50kV.) Never store materials and equipment under or near over- head powerlines. You need to recognize thatOperating a crane near overhead wires is overhead powerlines are a hazard.very hazardous. ive workers were constructing a chain-link fence in front of a F house, directly below a 7,200-volt energized powerline. As they prepared to install 21-foot sections of metal top rail on the fence, one of the workers picked up a section of rail and held it up vertically. The rail contacted the 7,200-volt line, and the worker was electrocuted. Following inspection, OSHA determined that the employee who was killed had never received any safety training from his employer and no specific instruction on how to avoid the hazards associated with overhead powerlines. In this case, the company failed to obey these regulations: • Employers must train their workers to recognize and avoid unsafe conditions on the job. • Employers must not allow their workers to work near any part of an electrical circuit UNLESS the circuit is de-energized (shut off) and grounded, or guarded in such a way that it cannot be con- tacted. • Ground-fault protection must be provided at construction sites to guard against electrical shock. Defective insulation hazards Insulation that is defective or inadequate is an electrical hazard. Usually, a plastic or rubber covering insulates wires. Insulation prevents conductors from coming in contact with each„ insulation—material that does not conduct electricity easily other. Insulation also prevents conductors from coming in contact with people.Page 26 Section 5
  • 34. —RECOGNIZING HAZARDS Extension cords may have damaged insulation. Sometimes the insu- lation inside an electrical tool or appliance is damaged. When insula- tion is damaged, exposed metal parts may become energized if a live wire inside touches them. Electric hand tools that are old, damaged, or misused may have damaged insulation inside. If „ If you touch a damaged live power you touch damaged power tools tool, you will be shocked! or other equipment, you will receive a shock. You are more likely to receive a shock if the „ A damaged live power tool that is tool is not grounded or double- not grounded or double-insulated insulated. (Double-insulated is very dangerous! tools have two insulation barri- ers and no exposed metal parts.) You need to recognize that defective insulation is a hazard. This extension cord is damaged and should not be used. Improper grounding hazards When an electrical system is not grounded properly, a hazard exists. The most common OSHA electrical violation is improper grounding of equipment and circuitry. The metal parts of an electrical wiring system that we touch (switch plates, ceiling light fixtures, conduit, etc.) should be grounded and at 0 volts. If the system is not grounded properly, these parts may become energized. Metal parts of motors, appliances, or electronics that are plugged into improperly grounded circuits may be energized. When a circuit is not grounded properly, a hazard exists because unwanted voltage cannot be safely eliminated. „ fault current—any current that is not If there is no safe path to ground for fault currents, exposed metal in its intended path parts in damaged appliances can become energized. Extension cords may not provide a continuous path to ground „ ground potential—the voltage a because of a broken ground wire or plug. If you contact a defective grounded part should have; 0 volts relative to ground Section 5 Page 27
  • 35. S A F E T Y M O D E L S TA G E 1„ If you touch a defective live electrical device that is not grounded (or grounded improperly), you component that is not grounded, will be shocked. You need to recognize that an improperly grounded you will be shocked. electrical system is a hazard. Electrical systems are often grounded to metal water pipes that serve as a continuous path to ground. If plumbing is used as a path to ground for fault current, all pipes must be made of conductive material (a type of metal). Many electrocutions and fires occur because (during renova- tion or repair) parts of metal plumbing are replaced with plastic pipe, which does not conduct electricity. In these cases, the path to ground is interrupted by nonconductive material.„ GFCI—ground fault circuit A ground fault circuit interrupter, or GFCI, is an inexpensive life- interrupter—a device that detects saver. GFCI’s detect any difference in current between the two circuit current leakage from a circuit to wires (the black wires and white wires). This differ- ground and shuts the current off ence in current could happen when electrical equipment is not working correctly,„ leakage current—current that does causing leakage current. If leakage not return through the intended path current (a ground fault) is detected in a GFCI receptacle. but instead "leaks” to ground GFCI-protected circuit, the GFCI switches„ ground fault—a loss of current from a circuit to a ground connection off the current in the circuit, protecting you from a dangerous shock. GFCI’s are set at about 5 mA and are designed to protect workers from electrocution. GFCI’s are able to detect the loss of current resulting from leakage through a person who is beginning to be shocked. If this situation occurs, the GFCI switches off the current in the circuit. GFCI’s are different from circuit breakers because they detect leakage currents rather than overloads. Circuits with missing, damaged, or improperly wired GFCI’s may allow you to be shocked. You need to recognize that a circuit improperly protected by a GFCI is a hazard. Overload hazards„ overload—too much current in a circuit Overloads in an electrical system are hazardous because they can produce heat or arcing. Wires and other components„ An overload can lead to a fire or in an electrical system or circuit have a electrical shock. maximum amount of current they can carry safely. If too many devices are plugged into a circuit, the electrical cur- rent will heat the wires to a very high temperature. If any one tool uses too Overloads are a major cause much current, the wires will heat up. of fires.Page 28 Section 5
  • 36. —RECOGNIZING HAZARDS The temperature of the wires can be high enough to cause a fire. If their insulation melts, arcing may occur. Arcing can cause a fire in the area where the overload exists, even inside a wall. „ circuit breaker—an overcurrent In order to prevent too much current in a circuit, a circuit breaker or protection device that automatically shuts off the current in a circuit if an fuse is placed in the circuit. If there is too much current in the cir- overload occurs cuit, the breaker “trips” and opens like a switch. If an overloaded „ trip—the automatic opening circuit is equipped with a fuse, an internal part of the fuse melts, (turning off) of a circuit by a GFCI or opening the circuit. Both breakers and fuses do the same thing: open circuit breaker the circuit to shut off the electrical current. „ fuse—an overcurrent protection If the breakers or fuses are too big for the wires they are supposed to device that has an internal part that protect, an overload in the circuit will not be detected and the cur- melts and shuts off the current in a rent will not be shut off. Overloading leads to overheating of circuit circuit if there is an overload components (including wires) and may cause a fire. You need to „ Circuit breakers and fuses that recognize that a circuit with improper overcurrent protection are too big for the circuit are dangerous. devices—or one with no overcurrent protection devices at all— „ Circuits without circuit breakers or is a hazard. fuses are dangerous. Overcurrent protection devices are built into the wiring of some electric motors, tools, and electronic devices. For example, if a tool draws too much current or if it overheats, the current will be shut off from within the device itself. Damaged tools can overheat and cause „ Damaged power tools can cause a fire. You need to recognize that a damaged tool is a hazard. overloads. Damaged equipment can overheat and cause a fire. Wet conditions hazards Working in wet conditions is hazardous because you may become an easy path for electrical current. If you touch a live wire or other „ Wet conditions are dangerous. electrical component—and you are well-grounded because you are standing in even a small puddle of water—you will receive a shock. Section 5 Page 29
  • 37. S A F E T Y M O D E L S TA G E 1 Damaged insulation, equipment, or tools can expose you to live electrical parts. A damaged tool may not be grounded properly, so the housing of the tool may be energized, causing you to receive a shock. Improperly grounded metal switch plates and ceiling lights are especially hazardous in wet conditions. If you touch a live elec- trical component with an uninsulated hand tool, you are more likely to receive a shock when standing in water. But remember: you don’t have to be standing in water to be electro- cuted. Wet clothing, high humidity, and perspiration also increase your chances of being electrocuted. You need to recognize that all wet conditions are hazards.„ An electrical circuit in a damp place without a GFCI is dangerous! A GFCI reduces the danger. Additional hazards In addition to electrical hazards, other types of hazards are present at job sites. Remember that all of these hazards can be controlled.„ There are non-electrical hazards at job sites, too. u There may be chemical hazards. Solvents and other substances may be poisonous or cause disease. u Frequent overhead work can cause tendinitis (inflammation) in your shoulders. Overhead work can cause long-term shoulder pain.Page 30 Section 5
  • 38. —RECOGNIZING HAZARDS u Intensive use of hand tools that involve force or twisting can cause tendinitis of the hands, wrists, or elbows. Use of hand tools can also cause carpal tunnel syndrome, which results when nerves in the wrist are damaged by swelling tendons or contract- ing muscles. Frequent use of some hand tools can cause wrist problems such as carpal tunnel syndrome. 22-year-old carpenter’s apprentice was killed when he was struck in the head by a nail A fired from a powder-actuated nail gun (a device that uses a gun powder cartridge to drive nails into concrete or steel). The nail gun operator fired the gun while attempting to anchor a plywood concrete form, causing the nail to pass through the hollow form. The nail traveled 27 feet before striking the victim. The nail gun operator had never received training on how to use the tool, and none of the employees in the area was wearing PPE. In another situation, two workers were building a wall while remodeling a house. One of the workers was killed when he was struck by a nail fired from a powder-actuated nail gun. The tool operator who fired the nail was trying to attach a piece of plywood to a wooden stud. But the nail shot though the plywood and stud, striking the victim. Below are some OSHA regulations that should have been followed. • Employees using powder- or pressure-actuated tools must be trained to use them safely. „PPE—personal protective • Employees who operate powder- or pressure-actuated tools must be trained to avoid firing equipment (eye protection, into easily penetrated materials (like plywood). hard hat, special clothing, • In areas where workers could be exposed to flying nails, appropriate PPE must be used. etc.) Section 5 Page 31
  • 39. S A F E T Y M O D E L S TA G E 1 u Low back pain can result from lifting objects the wrong way or carrying heavy loads of wire or other material. Back pain can also occur as a result of injury from poor working surfaces such as wet or slippery floors. Back pain is common, but it can be dis- abling and can affect young individuals. u Chips and particles flying from tools can injure your eyes. Wear eye protection. u Falling objects can hit you. Wear a hard hat. u Sharp tools and power equipment can cause cuts and other injuries. If you receive a shock, you may react and be hurt by a tool. u You can be injured or killed by falling from a ladder or scaffold- ing. If you receive a shock—even a mild one—you may lose your balance and fall. Even without being shocked, you could Lift with your legs, not fall from a ladder or scaffolding. your back! u You expose yourself to hazards when you do not wear PPE. All of these situations need to be recognized as hazards. You need to be especially careful when working on scaffolding or ladders.Page 32 Section 5
  • 40. —RECOGNIZING HAZARDS Summary of Section 5 You need to be able to recognize that electrical shocks, fires, or falls result from these hazards: Inadequate wiring Exposed electrical parts Overhead powerlines Defective insulation Improper grounding Overloaded circuits Wet conditions Damaged tools and equipment Improper PPE Section 5 Page 33
  • 41. S A F E T Y M O D E L S TA G E Section 6 Safety Model Stage 2— Evaluating Hazards How Do You Evaluate Your Risk? „ risk—the chance that injury or After you recognize a hazard, your next step is to evaluate your risk death will occur from the hazard. Obviously, exposed wires should be recognized as a hazard. If the exposed wires are 15 feet off the ground, your risk is low. However, if you are going to be working on a roof near those same wires, your risk is high. The risk of shock is greater if you will be carrying metal conduit that could touch the exposed wires. You „ Make the right decisions. must constantly evaluate your risk. Combinations of hazards increase your risk. Improper grounding and a damaged tool greatly increase your risk. Wet conditions com- bined with other hazards also increase your risk. You will need to make decisions about the nature of hazards in order to evaluate your risk and do the right thing to remain safe. There are “clues” that electrical hazards exist. For example, if a GFCI keeps tripping while you are using a power tool, there is a problem. Don’t keep resetting the GFCI and continue to work. You must evaluate the “clue” and decide what action should be taken to control the hazard. There are a number of other conditions that indi-Combinations of hazards increase risk. cate a hazard. u Tripped circuit breakers and blown fuses show that too much „ short—a low-resistance path current is flowing in a circuit. This condition could be due to sev- between a live wire and the eral factors, such as malfunctioning equipment or a short between ground, or between wires at conductors. You need to determine the cause in order to control different voltages (called a fault if the current is unintended) the hazard. u An electrical tool, appliance, wire, or connection that feels warm may indicate too much current in the circuit or equipment. You need to evaluate the situation and determine your risk. u An extension cord that feels warm may indicate too much current for the wire size of the cord. You must decide when action needs to be taken. Page 34 Section 6
  • 42. 2 — E VA L U AT I N G H A Z A R D S u A cable, fuse box, or junction box that feels warm may indicate Any of these conditions, or too much current in the circuits. “clues,” tells you something important: there is a risk of fire u A burning odor may indicate overheated insulation. and electrical shock. The equip- u Worn, frayed, or damaged insulation around any wire or other ment or tools involved must be conductor is an electrical hazard because the conductors could be avoided. You will frequently be exposed. Contact with an exposed wire could cause a shock. caught in situations where you Damaged insulation could cause a short, leading to arcing or a need to decide if these clues are fire. Inspect all insulation for scrapes and breaks. You need to present. A maintenance electri- evaluate the seriousness of any damage you find and decide how cian, supervisor, or instructor to deal with the hazard. needs to be called if there are signs of overload and you are not u A GFCI that trips indicates there is current leakage from the cir- sure of the degree of risk. Ask for cuit. First, you must decide the probable cause of the leakage by help whenever you are not sure recognizing any contributing hazards. Then, you must decide what to do. By asking for help, you what action needs to be taken. will protect yourself and others. Summary of Section 6 Look for “clues” that hazards are present. Evaluate the seriousness of hazards. Decide if you need to take action. Don’t ignore signs of trouble. n 18-year-old male worker, with 15 months of experience at a fast food restaurant, was plugging a toast- A er into a floor outlet when he received a shock. Since the restaurant was closed for the night, the floor had been mopped about 10 minutes before the incident. The restaurant manager and another employee heard the victim scream and investigated. The victim was found with one hand on the plug and the other hand grasping the metal receptacle box. His face was pressed against the top of the outlet. An employee tried to take the victim’s pulse but was shocked. The manager could not locate the correct breaker for the circuit. He then called the emergency squad, returned to the breaker box, and found the correct breaker. By the time the circuit was opened (turned off), the victim had been exposed to the current for 3 to 8 minutes. The employee checked the victim’s pulse again and found that it was very rapid. The manager and the employee left the victim to unlock the front door and place another call for help. Another employee arrived at the restaurant and found that the victim no longer had a pulse. The employee began administering CPR, which was continued by the rescue squad for 90 minutes. The victim was dead on arrival at a local hospital. Later, two electricians evaluated the circuit and found no serious problems. An investigation showed that the victim’s hand slipped forward when he was plugging in the toaster. His index finger made contact with an energized prong in the plug. His other hand was on the metal receptacle box, which was grounded. Current entered his body through his index finger, flowed across his chest, and exited through the other hand, which was in contact with the grounded receptacle. To prevent death or injury, you must recognize hazards and take the right action. • If the circuit had been equipped with a GFCI, the current would have been shut off before injury occurred. • The recent mopping increased the risk of electrocution. Never work in wet or damp areas! Section 6 Page 35
  • 43. S A F E T Y M O D E L S TA G E 3 — C O N T R O L L I N G Section 7 Safety Model Stage 3— Controlling Hazards: Safe Work Environment How Do You Control Hazards? In order to control hazards, you must first create a safe work envi- ronment, then work in a safe manner. Generally, it is best to remove the hazards altogether and create an environment that is truly safe. When OSHA regulations and the NEC are followed, safe work envi- ronments are created. But, you never know when materials or equipment might fail. Prepare yourself for the unexpected by using safe work practices. Use as many safeguards as possible. If one fails, another may pro- tect you from injury or death. How Do You Create a Safe Work Environment?„ Guard against contact with A safe work environment is created by controlling contact with elec- electrical voltages and control trical voltages and the currents they can cause. Electrical currents electrical currents to create a need to be controlled so they do not pass through the body. In addi- safe work environment. tion to preventing shocks, a safe work environment reduces the chance of fires, burns, and falls. You need to guard against contact with electrical voltages and con- trol electrical currents in order to create a safe work environment. Make your environment safer by doing the following: u Treat all conductors—even “de-energized” ones—as if they are energized until they are locked out and tagged. u Lock out and tag out circuits and machines. u Prevent overloaded wiring by using the right size and type of wire. u Prevent exposure to live electrical parts by isolating them. u Prevent exposure to live wires and parts by using insulation. u Prevent shocking currents from electrical systems and tools by grounding them. u Prevent shocking currents by using GFCI’s. u Prevent too much current in circuits by using overcurrent protection devices.Page 36 Section 7
  • 44. HAZARDS: SAFE WORK ENVIRONMENT t about 1:45 a.m., two journeyman electricians began replacing bulbs and making repairs on light A fixtures in a spray paint booth at an automobile assembly plant. The job required the two electricians to climb on top of the booth and work from above. The top of the booth was filled with pipes and ducts that restricted visibility and movement. Flashlights were required. The electricians started at opposite ends of the booth. One electrician saw a flash of light, but continued to work for about 5 minutes, then climbed down for some wire. While cutting the wire, he smelled a burn- ing odor and called to the other electrician. When no one answered, he climbed back on top of the booth. He found his co-worker in contact with a single-strand wire from one of the lights. Needle-nose wire strip- pers were stuck in the left side of the victim’s chest. Apparently, he had been stripping insulation from an improperly grounded 530-volt, single-strand wire when he contacted it with the stripper. In this case, the electricians knew they were working on energized circuits. The breakers in the booth’s control panel were not labeled and the lock used for lock-out/tag-out was broken. The surviving electrician stated that locat- ing the means to de-energize a circuit often takes more time than the actual job. The electrician would be alive today if the following rules had been observed. • Always shut off circuits—then test to confirm that they are de-energized—before starting a job. • Switchgear that shuts off a circuit must be clearly labeled and easy to access. • Lock-out/tag-out materials must always be provided, and lock-out/tag-out procedures must always be followed. Lock out and tag out circuits and equipment Create a safe work environment by locking out and tagging out circuits and machines. Before working on a circuit, you must turn off the power supply. Once the circuit has been shut off and de-energized, lock out the switchgear to the circuit so the power cannot be turned back on inadvertently. Then, tag out the circuit with an easy-to-see sign or label that lets everyone know that you are working on the circuit. If you are working on or near machinery, you must lock out and tag out the machinery to prevent startup. Before you begin work, you must test the circuit to make sure it is de-energized. Always test a circuit to make sure it is Lock-out/tag-out saves lives. de-energized before working on it. Section 7 Page 37
  • 45. S A F E T Y M O D E L S TA G E 3 — C O N T R O L L I N G Lock-Out/Tag-Out ChecklistLock-out/tag-out is an essential safety procedurethat protects workers from injury while working onor near electrical circuits and equipment. Lock-outinvolves applying a physical lock to the powersource(s) of circuits and equipment after they havebeen shut off and de-energized. The source is thentagged out with an easy-to-read tag that alerts otherworkers in the area that a lock has been applied.I n addition to protecting workers from electri- When performing lock-out/tag-out on circuits cal hazards, lock-out/tag-out prevents contact and equipment, you can use the checklist below. with operating equipment parts: blades, gears, Identify all sources of electrical energy for theshafts, presses, etc. equipment or circuits in question. Disable backup energy sources such as gener- A worker was replacing a V-belt on a dust collector ators and batteries. blower. Before beginning work, he shut down the unit at the local switch. However, an operator in the Identify all shut-offs for each energy source. control room restarted the unit using a remote Notify all personnel that equipment and switch. The worker’s hand was caught between the circuitry must be shut off, locked out, and pulley and belts of the blower, resulting in cuts and tagged out. (Simply turning a switch off is a fractured finger. NOT enough.) When performing lock-out/tag-out on machinery, Shut off energy sources and lock switchgear you must always lock out and tag out ALL energy sources leading to the machinery. in the OFF position. Each worker should apply his or her individual lock. Do not giveAlso, lock-out/tag-out prevents the unexpected your key to anyone.release of hazardous gasses, fluids, or solid matter Test equipment and circuitry to make surein areas where workers are present. they are de-energized. This must be done by a qualified person.* An employee was cutting into a metal pipe using a Deplete stored energy by bleeding, blocking, blowtorch. Diesel fuel was mistakenly discharged grounding, etc. into the line and was ignited by his torch. The Apply a tag to alert other workers that an worker burned to death at the scene. energy source or piece of equipment has been All valves along the line should have been locked locked out. out, blanked out, and tagged out to prevent the release of fuel. Blanking is the process of inserting Make sure everyone is safe and accounted for a metal disk into the space between two pipe before equipment and circuits are unlocked flanges. The disk, or blank, is then bolted in place and turned back on. Note that only a qualified to prevent passage of liquids or gasses through person may determine when it is safe to re- the pipe. energize circuits. *OSHA defines a “qualified person” as someone who has received mandated training on the hazards and on the construction and operation of equipment involved in a task.Page 38 Section 7
  • 46. HAZARDS: SAFE WORK ENVIRONMENT Control inadequate wiring hazards Electrical hazards result from using the wrong size or type of wire. „ Use the right size and type of You must control such hazards to create a safe work environment. wire. You must choose the right size wire for the amount of current „ AWG—American Wire Gauge— a measure of wire size expected in a circuit. The wire must be able to handle the current safely. The wire’s insulation must be appropriate for the voltage and tough enough for the environment. Connections need to be reliable and protected. 14 AWG 12 AWG 12 AWG 10 AWG 8 AWG 6 AWG 2 AWG 1/0 AWG (stranded) (solid) 20 amps 25 amps 30 amps 40 amps 55 amps 95 amps 125 amps Wires come in different sizes. The maximum current each size can conduct safely is shown. Section 7 Page 39
  • 47. S A F E T Y M O D E L S TA G E 3 — C O N T R O L L I N G Control hazards of fixed wiring The wiring methods and size of conductors used in a system depend on several factors: u Intended use of the circuit system u Building materials u Size and distribution of electrical load u Location of equipment (such as underground burial) u Environmental conditions (such as dampness) u Presence of corrosives u Temperature extremes „ fixed wiring—the permanent Fixed, permanent wiring is better than extension cords, which can be wiring installed in homes and misused and damaged more easily. NEC requirements for fixed other buildings wiring should always be followed. A variety of materials can be used in wiring applications, including nonmetallic sheathed cable (Romex®), armored cable, and metal and plastic conduit. The choice of wiring material depends on the wiring environment and the need to support and protect wires. Aluminum wire and connections should be handled with special care. Connections made with aluminum wire can loosen due to heat expansion and oxidize if they are not made properly. Loose or oxidized connections can create heat or arcing. Special clamps and terminals are necessary to make proper connections using aluminum wire. Antioxidant paste can be applied to connections to prevent oxidation. Control hazards of flexible wiring Use flexible wiring properly Electrical cords supplement fixed wiring by providing the flexibility required for maintenance, portability, isolation from vibration, and emergency and temporary power needs.Nonmetalic sheathing helps protectwires from damage. Page 40 Section 7
  • 48. HAZARDS: SAFE WORK ENVIRONMENT Flexible wiring can be used for extension cords or power supply „ flexible wiring—cables with cords. Power supply cords can be removable or permanently insulated and stranded wire that bends easily attached to the appliance. 29-year-old male welder was assigned to work on an outdoor concrete platform attached to the A main factory building. He wheeled a portable arc welder onto the platform. Since there was not an electrical outlet nearby, he used an extension cord to plug in the welder. The male end of the cord had four prongs, and the female end was spring-loaded. The worker plugged the male end of the cord into the outlet. He then plugged the portable welder’s power cord into the female end of the extension cord. At that instant, the metal case around the power cord plug became energized, electrocuting the worker. An investigation showed that the female end of the extension cord was broken. The spring, cover plate, and part of the casing were missing from the face of the female connector. Also, the grounding prong on the welder’s power cord plug was so severely bent that it slipped outside of the connection. Therefore, the arc welder was not grounded. Normally, it would have been impossible to insert the plug incorrectly. But, since the cord’s female end was damaged, the “bad” connection was able to occur. Do not let this happen to you. Use these safe practices: • Thoroughly inspect all electrical equipment before beginning work. • Do not use extension cords as a substitute for fixed wiring. In this case, a weatherproof receptacle should have been installed on the platform. • Use connectors that are designed to stand up to the abuse of the job. Connectors designed for light-duty use should not be used in an industrial environment. DO NOT use flexible wiring in situations where frequent inspection would be difficult, where damage would be likely, or where long- „ Don’t use flexible wiring where it may get damaged. term electrical supply is needed. Flexible cords cannot be used as a substitute for the fixed wiring of a structure. Flexible cords must not be . . . u run through holes in walls, ceilings, or floors; u run through doorways, windows, or similar openings (unless physically protected); u attached to building surfaces (except with a tension take-up device within 6 feet of the supply end); u hidden in walls, ceilings, or floors; or u hidden in conduit or other raceways. Section 7 Page 41
  • 49. S A F E T Y M O D E L S TA G E 3 — C O N T R O L L I N G Use the right extension cord The size of wire in an extension cord must be compatible with the amount of current the cord will be expected to carry. The amount of current depends on the equipment plugged into the extension cord. Current ratings (how much current a device needs to operate) are„ power—the amount of energy used often printed on the nameplate. If a power rating is given, it is neces- in a second, measured in watts sary to divide the power rating in watts by the voltage to find the cur- rent rating. For example, a 1,000-watt heater plugged into a 120-volt circuit will need almost 10 amps of current. Let’s look at another„ 1 horsepower = 746 watts. example: A 1-horsepower electric motor uses electrical energy at the rate of almost 750 watts, so it will need a minimum of about 7 amps of current on a 120-volt circuit. But, electric motors need additional current as they startup or if they stall, requiring up to 200% of the nameplate current rating. Therefore, the motor would need 14 amps. Add to find the total current needed to operate all the appliances supplied by the cord. Choose a wire size that can handle the total current. American Wire Gauge (AWG) Wire size Handles up to #10 AWG 30 amps #12 AWG 25 amps #14 AWG 18 amps #16 AWG 13 amps Remember: The larger the gauge number, the smaller the wire!„ Do not use extension cords that The length of the extension cord also needs to be considered when are too long for the size of wire. selecting the wire size. Voltage drops over the length of a cord. If a cord is too long, the voltage drop can be enough to damage equip- ment. Many electric motors only operate safely in a narrow range of voltages and will not work properly at voltages different than the voltage listed on the nameplate. Even though light bulbs operate (somewhat dimmer) at lowered voltages, do not assume electric motors will work correctly at less-than-required voltages. Also, when electric motors start or operate under load, they require more current. The larger the size of the wire, the longer a cord can be without causing a voltage drop that could damage tools and equipment.Page 42 Section 7
  • 50. HAZARDS: SAFE WORK ENVIRONMENT The grounding path for extension cords must be kept intact to keep „ Make sure the path to ground is continuous. you safe. A typical extension cord grounding system has four components: u a third wire in the cord, called a ground wire; u a three-prong plug with a grounding prong on one end of the cord; u a three-wire, grounding-type receptacle at the other end of the cord; and u a properly grounded outlet. Outlets must be Control hazards of exposed live electrical grounded properly. parts: isolate energized components Electrical hazards exist when wires or other electrical parts are exposed. These hazards need to be controlled to create a safe work environment. Isolation of energized electrical parts makes them inac- cessible unless tools and special effort are used. Isolation can be accomplished by placing the energized parts at least 8 feet high and out of reach, or by guarding. Guarding is a type of isolation that uses various structures—like cabinets, boxes, screens, barriers, covers, and „ guarding—a covering or barrier that separates you from live partitions—to close-off live electrical parts. electrical parts This exposed electrical equipment is guarded by an 8-foot fence. Use covers to prevent accidental contact with electrical circuits. Section 7 Page 43
  • 51. S A F E T Y M O D E L S TA G E 3 — C O N T R O L L I N G 20-year-old male laborer was carrying a 20-foot piece of iron from a welding shop to an outside A storage rack. As he was turning a corner near a bank of electrical transformers, the top end of the piece of iron struck an uninsulated supply wire at the top of a transformer. Although the trans- formers were surrounded by a 6-foot fence, they were about 3 feet taller than the fence enclosure. Each transformer carried 4,160 volts. When the iron hit the supply wire, the laborer was electrocuted. A forklift operator heard the iron drop to the ground at about 8:46 a.m. and found the victim 5 minutes later. He was pronounced dead on arrival at a local hospital. • According to OSHA, the enclosure around the transformers was too short. The fence should have been at least 8 feet tall. • The company in this case did not offer any formal safety training to its workers. All employers should develop safety and health training programs so their employees know how to recognize and avoid life- threatening hazards. Take the following precautions to prevent injuries from contact with live parts: u Immediately report exposed live parts to a supervisor or teacher. As a student, you should never attempt to correct the condition yourself without supervision. u Provide guards or barriers if live parts cannot be enclosed completely. u Use covers, screens, or partitions for guarding that require tools to remove them. u Replace covers that have been removed from panels, motors, or fuse boxes. u Even when live parts are elevated to the required height (8 feet), care should be taken when using objects (like metal rods or pipes) that can contact these parts.This cover cannot be removed u Close unused conduit openings in boxes so that foreign objectswithout special tools. (pencils, metal chips, conductive debris, etc.) cannot get inside and damage the circuit. Control hazards of exposure to live electrical wires: use proper insulation Insulation is made of material that does not conduct electricity (usually plastic, rubber, or fiber). Insulation covers wires and prevents Page 44 Section 7
  • 52. HAZARDS: SAFE WORK ENVIRONMENT conductors from coming in contact with each other or any other conductor. If conductors are allowed to make contact, a short circuit is created. In a short circuit, current passes through the shorting material without passing through a load in the circuit, and the wire becomes overheated. Insulation keeps wires and other conductors from touching, which prevents electrical short circuits. Insulation prevents live wires from touching people and animals, thus protect- ing them from electrical shock. 29-year-old male maintenance worker was found at 3:45 a.m. lying on his back and convulsing. A Beside him were an overturned cart and an electric welding machine, both lying in a pool of water on the concrete floor. Arcing was visible between the welding machine and the floor. The worker was transported to the closest hospital, where he was pronounced dead. An examination of the welding machine showed that there were exposed conductors in the machine’s cables. There were numerous cuts and scrapes in the cables’ insulation. On other parts of the machine, insulation was damaged or missing. Also, the machine did not have a ground connection. Investigators concluded that the maintenance worker was electrocuted when he tried to turn off the weld- ing machine, which was sitting on the cart. The metal frame of the machine had become energized due to the damaged insulation. When he touched the energized frame, he completed the conducting path to ground. The current traveled through his body to ground. Since he was probably standing in water, the risk of a ground fault was even greater. You must take steps to decrease such hazards in your workplace: • Ground circuits and equipment. • Keep all equipment in good operating condition with a preventive maintenance program. • Never use electrical equipment or work on circuits in wet areas. If you find water or dampness, notify your supervisor immediately. Insulation helps protect wires from physical damage and conditions in the environment. Insulation is used on almost all wires, except some ground wires and some high-voltage transmission lines. Insulation is used internally in tools, switches, plugs, and other elec- trical and electronic devices. Special insulation is used on wires and cables that are used in harsh environments. Wires and cables that are buried in soil must have an outer covering of insulation that is flame-retardant and resistant to moisture, fungus, and corrosion. In all situations, you must be careful not to damage insulation while installing it. Do not allow staples or other supports to damage the „ Make sure insulation is the right insulation. Bends in a cable must have an inside radius of at least type and in good condition. Section 7 Page 45
  • 53. S A F E T Y M O D E L S TA G E 3 — C O N T R O L L I N G 5 times the diameter of the cable so that insulation at a bend is not damaged. Extension cords come with insulation in a variety of types and colors. The insulation of extension cords is especially important. Since extension cords often receive rough handling, the insulation can be damaged. Extension cords might be used in wet places, so adequate insulation is necessary to prevent shocks. Because exten- sion cords are often used near combustible materials (such as wood shavings and sawdust) a short in an extension cord could easily cause arcing and a fire. Insulation on individual wires is often color-coded. In general, insu- lated wires used as equipment grounding conductors are either con- tinuous green or green with yellow stripes. The grounded conductors that complete a circuit are generally covered with continuous white Arc-fault circuit or gray insulation. The ungrounded conductors, or “hot” wires, may breaker. be any color other than green, white, or gray. They are usually black or red. Conductors and cables must be marked by the manufacturer to show the following: u maximum voltage capacity, u AWG size, u insulation-type letter, and u the manufacturer’s name or trademark. Control hazards of shocking currents Ground circuits and equipment When an electrical system is not grounded properly, a hazard exists. This is because the parts of an electrical wiring system that a person normally touches may be energized, or live, relative to ground. Parts like switch plates, wiring boxes, conduit, cabinets, and lights need to be at 0 volts relative to ground. If the system is grounded improper- ly, these parts may be energized. The metal housings of equipment plugged into an outlet need to be grounded through the plug. Ground electrical devices.Page 46 Section 7
  • 54. HAZARDS: SAFE WORK ENVIRONMENT Grounding is connecting an electrical system to the earth with a wire. Excess or stray current travels through this wire to a grounding device (commonly called a “ground”) deep in the earth. Grounding prevents unwanted voltage on electrical components. Metal plumbing is often used as a ground. When plumbing is used as a grounding conductor, it must also be connected to a grounding device such as a conductive rod. (Rods used for grounding must be driven at least 8 feet into the earth.) Sometimes an electrical system will receive a higher voltage than it is designed to handle. These high voltages may come from a lightning strike, line surge, or contact with a higher- voltage line. Sometimes a defect occurs in a device that allows exposed metal parts to become energized. Grounding will help Grounding rod in protect the person working on a system, the system itself, and others the earth. using tools or operating equipment connected to the system. The extra current produced by the excess voltage travels relatively safely to the earth. Grounding creates a path for currents produced by unintended voltages on exposed parts. These currents follow the grounding path, rather than passing through the body of someone who touches the energized equipment. However, if a grounding rod takes a direct hit from a lightning strike and is buried in sandy soil, the rod should be examined to make sure it will still function properly. The heat from a lightning strike can cause the sand to turn into glass, which is an insulator. A grounding rod must be in contact with damp soil to be effective. Leakage current occurs when an electrical current escapes from its intended path. Leakages are sometimes low-current faults that can Grounding-type receptacle. occur in all electrical equipment because of dirt, wear, damage, or moisture. A good grounding system should be able to carry off this leakage current. A ground fault occurs when current passes through the housing of an electrical device to ground. Proper grounding pro- tects against ground faults. Ground faults are usually caused by misuse of a tool or damage to its insulation. This damage allows a bare conductor to touch metal parts or the tool housing. When you ground a tool or electrical system, you create a low- resistance path to the earth (known as a ground connection). When done properly, this path has sufficient current-carrying capacity to eliminate voltages that may cause a dangerous shock. Grounding does not guarantee that you will not be shocked, injured, or killed from defective equipment. However, it greatly reduces the possibility. Section 7 Page 47
  • 55. S A F E T Y M O D E L S TA G E 3 — C O N T R O L L I N G Equipment needs to be grounded under any of these circumstances: u The equipment is within 8 feet vertically and 5 feet horizontally of the floor or walking surface. u The equipment is within 8 feet vertically and 5 feet horizontally of grounded metal objects you could touch. u The equipment is located in a wet or damp area and is not isolated. u The equipment is connected to a power supply by cord and plug and is not double-insulated. Use GFCI’s The use of GFCI’s has lowered the number of electrocutions dramat- ically. A GFCI is a fast-acting switch that detects any difference in current between two circuit conductors. If either conductor comes in contact—either directly or through part of your body—with a ground (a situation known as a ground fault), the GFCI opens the circuit in a fraction of a second. If a current as small as 4 to 6 mA does not pass through both wires properly, but instead leaks to the ground, the GFCI is tripped. The current is shut off. There is a more sensitive kind of GFCI called an isolation GFCI. If a circuit has an isolation GFCI, the ground fault current passes through an electronic sensing circuit in the GFCI. The electronic sensing circuit has enough resistance to limit current to as little as 2 mA, which is too low to cause a dangerous shock. GFCI’s are usually in the form of a duplex receptacle. They are also available in portable and plug-in designs and as circuit breakers that protect an entire branch circuit. GFCI’s can operate on both two- and three-wire ground systems. For a GFCI to work properly, the neutral conductor (white wire) must (1) be continuous, (2) have low resistance, and (3) have sufficient current-carrying capacity. GFCI’s help protect you from electrical shock by continuously mon- itoring the circuit. However, a GFCI does not protect a person from Portable GFCI. line-to-line hazards such as touching two “hot” wires (240 volts) at the same time or touching a “hot” and neutral wire at the same time. Also be aware that instantaneous currents can be high when a GFCI„ GFCI’s have their limitations. is tripped. A shock may still be felt. Your reaction to the shock could cause injury, perhaps from falling. Test GFCI’s regularly by pressing the “test” button. If the circuit does not turn off, the GFCI is faulty and must be replaced.Page 48 Section 7
  • 56. HAZARDS: SAFE WORK ENVIRONMENT female assistant manager of a swim club was instructed to add a certain chemical to the pool. She A went down into the pump room, barefoot. The room was below ground level, and the floor was covered with water. She filled a plastic drum with 35-40 gallons of water, then plugged a mixing motor into a 120-volt wall outlet and turned on the motor. The motor would be used to mix the water and the chemical, then the solution would be added to the pool. While adding the chemical to the water in the drum, she contacted the mixing motor with her left hand. Apparently, the motor had developed a ground fault. Because of the ground fault, the motor was energized, and she was electrocuted. A co-worker found the victim slumped over the drum with her face submerged in water. The co-worker tried to move the victim but was shocked. The assistant manager was dead on arrival at a local hospital. An investigation showed that the mixing motor was in poor condition. The grounding pin had been removed from the male end of the power cord, resulting in a faulty ground. The circuit was equipped with a GFCI, but it was not installed properly. A properly wired and functioning GFCI could have sensed the ground fault in the motor and de-energized the circuit. Take a look at what could have been done to prevent this death. • The employer should have kept the motor in better condition. Power cords should be inspected regularly, and any missing prongs should be replaced. • All pool-area electrical circuits should be installed by qualified electricians. • The victim should have worn insulating boots or shoes since she was handling electrical equipment. • The employer should have followed the law. The NEC requires that all pool-associated motors have a permanent grounding system. In this case, this regulation was not followed. Also, electrical equipment is not permitted in areas without proper drainage. • OSHA requires employers to provide a work environment free of safety and health hazards. The NEC requires that GFCI’s be used in these high-risk situations: u Electricity is used near water. u The user of electrical equipment is grounded (by touching grounded material). u Circuits are providing power to portable tools or outdoor receptacles. Install bonding jumpers around nonconductive u Temporary wiring or extension cords are used. material. Specifically, GFCI’s must be installed in bathrooms, garages, out- „ Use GFCI’s to help protect people door areas, crawl spaces, unfinished basements, kitchens, and near in damp areas. wet bars. Bond components to assure grounding path In order to assure a continuous, reliable electrical path to ground, a „ bonding—joining electrical parts to bonding jumper wire is used to make sure electrical parts are con- assure a conductive path nected. Some physical connections, like metal conduit coming into a Section 7 Page 49
  • 57. S A F E T Y M O D E L S TA G E 3 — C O N T R O L L I N G„ bonding jumper—the box, might not make a good electrical connection because of paint conductor used to connect or possible corrosion. To make a good electrical connection, a bond- parts to be bonded ing jumper needs to be installed. A metal cold water pipe that is part of a path to ground may need bonding jumpers around plastic antivibration devices, plastic water meters, or sections of plastic pipe. A bonding jumper is made of conductive material and is tightly connected to metal pipes with screws or clamps to bypass the plastic and assure a continuous grounding path. Bonding jumpers are necessary because plastic does not conduct electricity and would interrupt the path to ground. Additionally, interior metal plumbing must be bonded to the ground for electrical service equipment in order to keep all grounds at the same potential (0 volts). Even metal air ducts should be bonded to electrical service equipment. Control overload current hazards When a current exceeds the current rating of equipment or wiring, a hazard exists. The wiring in the circuit, equipment, or tool cannot handle the current without heating up or even melting. Not only will the wiring or tool be damaged, but the high temperature of the con- ductor can also cause a fire. To prevent this from happening, an overcurrent protection device (circuit breaker or fuse) is used in a circuit. These devices open a circuit automatically if they detect cur- rent in excess of the current rating of equipment or wiring. This excess current can be caused by an overload, short circuit, or high- level ground fault. Use overcurrent protection devices (circuit breakers or fuses) in circuits.Page 50 Section 7
  • 58. HAZARDS: SAFE WORK ENVIRONMENT Overcurrent protection devices are designed to protect equipment and structures from fire. They do not protect you from electrical shock! Overcurrent protection devices stop the flow of current in a circuit when the amperage is too high for the circuit. A circuit break- er or fuse will not stop the relatively small amount of current that can cause injury or death. Death can result from 20 mA (.020 amps) through the chest (see Section 2). A typical residential circuit break- er or fuse will not shut off the circuit until a current of more than 20 amps is reached! But overcurrent protection devices are not allowed in areas where they could be exposed to physical damage or in hazardous environ- ments. Overcurrent protection devices can heat up and occasionally arc or spark, which could cause a fire or an explosion in certain areas. Hazardous environments are places that contain flammable or explosive materials such as flammable gasses or vapors (Class I Hazardous Environments), finely pulverized flammable dusts (Class II Hazardous Environments), or fibers or metal filings that can catch fire easily (Class III Hazardous Environments). Hazardous environments may be found in aircraft hangars, gas stations, storage plants for flammable liquids, grain silos, and mills where cotton fibers may be suspended in the air. Special electrical systems are required in hazardous environments. If an overcurrent protection device opens a circuit, there may be a problem along the circuit. (In the case of circuit breakers, frequent tripping may also indicate that the breaker is defective.) When a cir- cuit breaker trips or a fuse blows, the cause must be found. „ Find the cause of an overload. A circuit breaker is one kind of overcurrent protection device. It is a type of automatic switch located in a circuit. A circuit breaker trips when too much current passes through it. A circuit breaker should not be used regularly to turn power on or off in a circuit, unless the breaker is designed for this purpose and marked “SWD” (stands for “switching device”). A fuse is another type of overcurrent protection device. A fuse con- tains a metal conductor that has a relatively low melting point. When too much current passes through the metal in the fuse, it heats up within a fraction of a second and melts, opening the circuit. After an overload is found and corrected, a blown fuse must be replaced with a new one of appropriate amperage. Only circuit breakers marked “SWD” should be used as switches. Section 7 Page 51
  • 59. S A F E T Y M O D E L S TA G E 3 — C O N T R O L L I N GSummary of Section 7Control contact with electrical voltages and control electrical currents to create a safe work environment. Lock out and tag out circuits and machines. Prevent overloaded wiring by using the right size and type of wire. Prevent exposure to live electrical parts by isolating them. Prevent exposure to live wires and parts by using insulation. Prevent shocking currents from electrical systems and tools by grounding them. Prevent shocking currents by using GFCI’s. Prevent too much current in circuits by using overcurrent protection devices.Page 52 Section 7
  • 60. HAZARDS: SAFE WORK ENVIRONMENT Section 7 Page 53
  • 61. S A F E T Y M O D E L S TA G E 3 — C O N T R O L L I N G Section 8 Safety Model Stage 3— Controlling Hazards: Safe Work Practices How Do You Work Safely? A safe work environment is not enough to control all electrical haz- ards. You must also work safely. Safe work practices help you con- trol your risk of injury or death from workplace hazards. If you are working on electrical circuits or with electrical tools and equipment, you need to use safe work practices. Before you begin a task, ask yourself: u What could go wrong? u Do I have the knowledge, tools, and experience to do this work safely? All workers should be very familiar with the safety procedures for their jobs. You must know how to use specific controls that help keep you safe. You must also use good judgment and common sense. Control electrical hazards through safe work practices. u Plan your work and plan for safety. u Avoid wet working conditions and other dangers. u Avoid overhead powerlines. u Use proper wiring and connectors. u Use and maintain tools properly. u Wear correct PPE.Page 54 Section 8
  • 62. H A Z A R D S : S A F E WO R K P R AC T I C E S Plan your work and plan for safety Take time to plan your work, by yourself and with others. Safety planning is an important part of any task. It takes effort to recognize, evaluate, and control hazards. If you are thinking about your work „ Plan to be safe. tasks or about what others think of you, it is hard to take the time to plan for safety. But, YOU MUST PLAN. 40-year-old male meter technician had just completed a 7-week basic lineman training course. He A worked as a meter technician during normal working hours and as a lineman during unplanned out- ages. One evening, he was called to repair a residential power outage. By the time he arrived at the site of the outage, he had already worked 2 hours of overtime and worked 14 straight hours the day before. At the site, a tree limb had fallen across an overhead powerline. The neutral wire in the line was severed, and the two energized 120-volt wires were disconnected. The worker removed the tree limb and climbed up a power pole to reconnect the three wires. He was wearing insulated gloves, a hard hat, and safety glasses. He prepared the wires to be connected. While handling the wires, one of the energized wires caught the cuff of his left glove and pulled the cuff down. The conductor contacted the victim’s forearm near the wrist. He was electrocuted and fell backwards. He was wearing a climbing belt, which left him hanging upside down from the pole. Paramedics arrived 5 minutes after the contact. The power company lowered his dead body 30 minutes later. Several factors may have contributed to this incident. Below are some ways to eliminate these risk factors. • Ask for assistance when you are assigned tasks that cannot be safely completed alone. The task assigned to the victim could not have been done safely by only one person. • Do not work overtime performing hazardous tasks that are not part of your normal assignments. • Employees should only be given tasks that they are qualified to perform. All employees below the journeyman level should be supervised. Planning with others is especially helpful. It allows you to coordi- „ Don’t work alone. nate your work and take advantage of what others know about iden- tifying and controlling hazards. The following is a list of some things to think about as you plan. u Work with a “buddy”—Do not work alone. Both of you should be trained in CPR. Both of you must know what to do in an emergency. u Know how to shut off and de-energize circuits—You must find where circuit breakers, fuses, and switches are located. Then, the circuits that you will be working on (even low-voltage circuits) MUST BE TURNED OFF! Test the circuits before beginning work to make sure they are completely de-energized. Section 8 Page 55
  • 63. S A F E T Y M O D E L S TA G E 3 — C O N T R O L L I N G u Plan to lock out and tag out circuits and equipment—Make certain all energy sources are locked out and tagged out before performing any work on an electrical circuit or electrical device. Working on energized (“hot”) circuits is one of the most danger- ous things any worker could do. If someone turns on a circuit without warning, you can be shocked, burned, or electrocuted. The unexpected starting of electrical equipment can cause severe injury or death. Before ANY work is done on a circuit, shut off the circuit, lock out and tag out the circuit at the distribution panel, then test the circuit to make sure it is de-energized. Before ANY equipment inspections or repairs—even on so-called low-voltage circuits—the current must be turned off at the switch box, and the switch must be padlocked in the OFF position. At the same time, the equipment must be securely tagged to warn everyone that work is being performed. Again, test circuits and equipment to ensure they are de-energized. This worker is No two locks should be alike. Each key should fit only one lock, applying a group and only one key should be issued to each worker. If more than lock-out device. The one worker is working on a circuit or repairing a piece of equip- equipment cannot ment, each worker should lock out the switch with his or her own be re-started until lock and never permit anyone else to remove it. At all times, you all workers remove must be certain that you are not exposing other workers to dan- their locks. ger. Workers who perform lock-out/tag-out must be trained and authorized to repair and maintain electrical equipment. A locked- out switch or feeder panel prevents others from turning on a cir- cuit. The tag informs other workers of your action. u Remove jewelry and metal objects—Remove jewelry and other metal objects or apparel from your body before beginning work. These things can cause burns if worn near high currents and can get caught as you work. u Plan to avoid falls—Injuries can result from falling off scaffold- ing or ladders. Other workers may also be injured from equip- ment and debris falling from scaffolding and ladders.Page 56 Section 8
  • 64. H A Z A R D S : S A F E WO R K P R AC T I C E S worker was attempting to correct an electrical problem involving two non-operational lamps. He A examined the circuit in the area where he thought the problem was located. He had not shut off the power at the circuit breaker panel and did not test the wires to see if they were live. He was elec- trocuted when he grabbed the two live wires with his left hand. He collapsed to the floor and was found dead. • Employers should not allow work to be done on electrical circuits unless an effective lock-out/tag-out program is in place. • No work should be done on energized electrical circuits. Circuits must be shut off, locked out, and tagged out. Even then, you must test the circuit before beginning work to confirm that it is de-energized (“dead”). 277 VOLT LAMPS FUSE BOX Section 8 Page 57
  • 65. Ladder Safety Fact SheetTo prevent injury when climbing, follow these procedures:1. Position the ladder at a safe angle to prevent slipping. The hori- zontal distance from the base of the ladder to the structure should be one-quarter the length of the ladder. If you don’t have a way to make this measurement, follow the steps below to determine if the ladder is positioned at a safe angle. Put your feet at the base of the ladder and extend your arms straight out. If you can touch the closest part of the ladder without bending your arms, the ladder is probably at the correct angle. If you have to bend your arms to touch the closest part of the ladder or if you can’t reach the ladder at all, the ladder is not positioned at a safe angle.2. Make sure the base of the ladder has firm support and the ground or floor is level. Be very careful when placing a ladder on wet, icy, or otherwise slippery surfaces. Special blocking may be needed to prevent slipping in these cases.3. Follow the manufacturer’s recommendations for proper use.4. Check the condition of the ladder before using it. Joints must be tight to prevent wobbling or leaning.Page 58 Section 8
  • 66. 5. When using a stepladder, make sure it is level and fully open. Always lock the hinges. Do not stand on or above the top step.6. When using scaffolding, use a ladder to access the tiers. Never climb the cross braces.7. Do not use metal ladders. Instead, use ladders made of fiberglass. (Although wooden ladders are permitted, wood can soak up water and become conductive.)8. Beware of overhead powerlines when you work with ladders and scaffolding. Learn how to use ladders and scaffolding properly.Section 8 Page 59
  • 67. S A F E T Y M O D E L S TA G E 3 — C O N T R O L L I N G crew of 7 workers was painting a 33-foot sign at a shopping mall. The crew used tubular A welded frame scaffolding that was 31 feet tall and made up of several tiers. The sign was partially painted when the crew was instructed to move the scaffolding so that concrete could be poured for an access road. The crew moved the scaffolding 30 feet without disassembling it. An overhead powerline was located about 10 feet away from the scaffolding. After the concrete hardened, the workers lift- ed the scaffolding to move it back to the sign. The top tier came loose, fell, and contacted the powerline. All seven workers were knocked away from the scaffolding. Two died; five were hospitalized. You must take certain precautions when working with scaffolding. • Scaffolding should not be moved until all potential safety hazards are identified and controlled. In this case, the scaffolding should have been taken apart before it was moved. • Locking pins must be used to secure tiers to one another. • Always make sure you have enough time to complete your assignment safely. If you are rushed, you may be more likely to take deadly short-cuts (such as failing to dismantle scaffolding before moving it). • Employers must have a written safety program that includes safe work procedures and hazard recognition. u Do not do any tasks that you are not trained to do or that you do not feel comfortable doing! company was contracted to install wiring and fixtures in a new office complex. The third floor was A being prepared in a hurry for a new tenant, and daily changes to the electrical system blueprints were arriving by fax. The light fixtures in the office were mounted in a metal grid that was fastened to the ceiling and properly grounded. A 23-year-old male apprentice electrician was working on a light fixture when he contacted an energized conductor. He came down from the fiberglass ladder and collapsed. Apparently, he had contacted the “hot” conductor while also in contact with the metal grid. Current passed through his body and into the ground- ed grid. Current always takes a path to ground. In this case, the worker was part of that path. He was dead on arrival at a nearby hospital. Later, an investigation showed that the victim had cross-wired the conductors in the fixture by mistake. This incorrect wiring allowed electricity to flow from a live circuit on the completed section of the building to the circuit on which the victim was working. Below are some safety procedures that should have been followed in this case. Because they were ignored, the job ended in death. • Before work begins, all circuits in the immediate work area must be shut off, locked out, and tagged out—then tested to confirm that they are de-energized. • Wiring done by apprentice electricians should be checked by a journeyman. • A supervisor should always review changes to an original blueprint in order to identify any new hazards that the changes might create.Page 60 Section 8
  • 68. H A Z A R D S : S A F E WO R K P R AC T I C E S Avoid wet working conditions and other dangers Remember that any hazard becomes much more dangerous in damp or wet conditions. To be on the safe side, assume there is dampness in any work location, even if you do not see water. Even sweat can create a damp condition! u Do not work wet—Do not work on circuits or use electrical „ Avoid wet conditions! Even avoid equipment in damp or wet areas. If necessary, clear the area of damp conditions! loose material or hanging objects. Cover wet floors with wooden planking that can be kept dry. Wear insulating rubber boots or shoes. Your hands must be dry when plugging and unplugging power cords and extension cords. Do not get cleaning solutions on energized equipment. u Use a GFCI—Always use a GFCI when using portable tools and extension cords. Avoid overhead powerlines Be very careful not to contact overhead powerlines or other exposed wires. More than half of all electrocutions are caused by contact with overhead lines. When working in an elevated position near overhead lines, avoid locations where you (and any conductive object you hold) could contact an unguarded or uninsulated line. You should be at least 10 feet away from high-voltage transmission lines. Vehicle operators should also pay attention to overhead wiring. Dump trucks, front-end loaders, and cranes can lift and make contact with overhead lines. If you contact equipment that is touching live wires, you will be shocked and may be killed. If you are in the vehicle, stay inside. Always be aware of what is going on around you. Use proper wiring and connectors Portable GFCI. u Avoid overloads—Do not overload circuits. u Test GFCI’s—Test GFCI’s monthly using the “test” button. Section 8 Page 61
  • 69. S A F E T Y M O D E L S TA G E 3 — C O N T R O L L I N G worker from an electrical service company was changing bulbs in pole-mounted light fixtures in a shop- A ping center parking lot. The procedure for installing the bulbs was as follows: The worker would park the truck near the first light pole. The truck was equipped with a roof-mounted ladder. The worker would extend the ladder high enough to change the bulb, then drive to the next pole without lowering the ladder. After the worker replaced the first bulb, he got back in the truck and drove toward the next light pole. As the truck moved along, a steel cable attached to the top of the ladder contacted an overhead powerline. The work- er realized something was wrong, stopped the truck, and stepped onto the pavement while still holding onto the door of the truck. By doing this, he completed the path to ground for the current in the truck. Because the ladder was still in contact with the powerline, the entire truck was now energized. He was engulfed in flames as the truck caught fire. Fire, police, and paramedic units arrived within 5 minutes. Utility workers arrived in about 10 minutes and de-energized (shut off) the powerline. The victim burned to death at the scene. Below are some ways to prevent contact with overhead powerlines. • A safe distance must be maintained between ladders (and other equipment) and overhead lines. OSHA requires that a clearance of at least 10 feet be maintained between aerial ladders and overhead powerlines of up to 50,000 volts. • Moving a truck with the ladder extended is a dangerous practice. One way to control this hazard is to install an engine lock that prevents a truck’s engine from starting unless the ladder is fully retracted. • If there are overhead powerlines in the immediate area, lighting systems that can be serviced from ground level are recommended for safety. • If the worker had been trained properly, he may have known to stay inside the truck. • Pre-job safety surveys should always be performed to identify and control hazards. In this case, a survey would have identified the powerlines as a possible hazard, and appropriate hazard control measures (such as lowering the ladder between installations) could have been taken. u Check switches and insulation—Tools and other equipment must operate properly. Make sure that switches and insulating parts are in good condition. u Use three-prong plugs—Never use a three-prong grounding plug with the third prong broken-off. When using tools that require a third-wire ground, use only three-wire extension cords with three-prong grounding plugs and three-hole electrical out- lets. Never remove the grounding prong from a plug! You could be shocked or expose someone else to a hazard. If you see a cord without a grounding prong in the plug, remove the cord from service immediately. u Use extension cords properly—If an extension cord must be used, choose one with sufficient ampacity for the tool being used. An undersized cord can overheat and cause a drop in voltage andNever use a three-pronggrounding plug with the third tool power. Check the tool manufacturer’s recommendations forprong broken off. the required wire gauge and cord length. Make sure the insulation is intact. To reduce the risk of damage to a cord’s insulation, usePage 62 Section 8
  • 70. H A Z A R D S : S A F E WO R K P R AC T I C E S cords with insulation marked “S” (hard service) rather than cords marked “SJ” (junior hard service). Make sure the grounding prong is intact. In damp locations, make sure wires and connec- tors are waterproof and approved for such locations. Do not create a tripping hazard. u Check power cords and extensions—Electrical cords should be inspected regularly using the following procedure: 1. Remove the cord from the electrical power source before inspecting. 2. Make sure the grounding prong is present in the plug. 3. Make sure the plug and receptacle are not damaged. 4. Wipe the cord clean with a diluted detergent and examine for cuts, breaks, abrasions, and defects in the insulation. 5. Coil or hang the cord for storage. Do not use any other methods. Coiling or hanging is the best way to avoid tight kinks, cuts, and scrapes that can damage insulation or conductors. You should also test electrical cords regularly for ground continuity using a continuity tester as follows: 1. Connect one lead of the tester to the ground prong at one end of the cord. 2. Connect the second lead to the ground wire hole at the other end of the cord. 3. If the tester lights up or beeps (depending on design), the cord’s ground wire is okay. If not, the cord is damaged and should not be used. u Do not pull on cords—Always disconnect a cord by the plug. u Use correct connectors—Use electrical plugs and receptacles that are right for your current and voltage needs. Connectors are designed for specific currents and voltages so that only matching plugs and receptacles will fit together. This safeguard prevents a piece of equipment, a cord, and a power source with different voltage and current requirements from being plugged together. Standard configurations for plugs and receptacles have been established by the National Electric Manufacturers Association (NEMA). Section 8 Page 63
  • 71. S A F E T Y M O D E L S TA G E 3 — C O N T R O L L I N G u Use locking connectors—Use locking-type attachment plugs, receptacles, and other connectors to prevent them from becoming unplugged. Use and maintain tools properlyLocking-type attachment plug. Your tools are at the heart of your craft. Tools help you do your job with a high degree of quality. Tools can do something else, too. They can cause injury or even death! You must use the right tools for the job. Proper maintenance of tools and other equipment is very important. Inadequate maintenance can cause equipment to deterio-„ Maintain tools and equipment. rate, creating dangerous conditions. You must take care of your tools so they can help you and not hurt you. u Inspect tools before using them—Check for cracked casings,„ Inspect your equipment before dents, missing or broken parts, and contamination (oil, moisture, you use it. dirt, corrosion). Damaged tools must be removed from service and properly tagged. These tools should not be used until they are repaired and tested. This cord has been spliced using a wire nut. Spliced cords are very dangerous!Page 64 Section 8
  • 72. H A Z A R D S : S A F E WO R K P R AC T I C E S n employee was climbing a metal ladder to hand an electric drill to the journeyman installer on A a scaffold about 5 feet above him. When the victim reached the third rung of the ladder, he received an electrical shock that killed him. An investigation showed that the grounding prong was missing from the extension cord attached to the drill. Also, the cord’s green grounding wire was, at times, contacting the energized black wire. Because of this contact with the "hot" wire, the entire length of the grounding wire and the drill’s frame became energized. The drill was not double-insulated. To avoid deadly incidents like this one, take these precautions: • Make certain that approved GFCI’s or equipment grounding systems are used at construction sites. • Use equipment that provides a permanent and continuous path to ground. Any fault current will be safely diverted along this path. • Inspect electrical tools and equipment daily and remove damaged or defective equipment from use right away. u Use the right tool correctly—Use tools correctly and for their intended purposes. Follow the safety instructions and operating „ Use the right tools and equipment. procedures recommended by the manufacturer. When working on a circuit, use approved tools with insulated handles. However, „ Do not work on energized circuits. DO NOT USE THESE TOOLS TO WORK ON ENERGIZED CIRCUITS. ALWAYS SHUT OFF AND DE-ENERGIZE CIRCUITS BEFORE BEGINNING WORK ON THEM. u Protect your tools—Keep tools and cords away from heat, oil, and sharp objects. These hazards can damage insulation. If a tool or cord heats up, stop using it! Report the condition to a supervi- sor or instructor immediately. If equipment has been repaired, make sure that it has been tested and certified as safe before using it. Never carry a tool by the cord. Disconnect cords by pulling the plug—not the cord! u Use double-insulated tools—Portable electrical tools are classi- fied by the number of insulation barriers between the electrical conductors in the tool and the worker. The NEC permits the use of portable tools only if they have been approved by Underwriter’s Laboratories (UL Listed). Equipment that has two insulation barriers and no exposed metal parts is called double- insulated. When used properly, double-insulated tools provide reliable shock protection without the need for a third ground Don’t work on energized circuits like this one! Always follow correct lock-out/tag-out procedures. Section 8 Page 65
  • 73. S A F E T Y M O D E L S TA G E 3 — C O N T R O L L I N G 22-year-old male carpenter was building the wooden framework of a laundry building. He was using A portable power tools. Electricity was supplied to the tools by a temporary service pole 50 feet away. The service pole had not been inspected and was not in compliance. It was also not grounded. The carpenter plugged a “homemade” cord into the service pole and then plugged a UL-approved cord into the homemade cord. His power saw was plugged into the UL-approved cord. The site was wet. Humidity was high and the carpenter was sweating. Reportedly, he was mildly shocked throughout the morning and replaced the extension cord he was using in an effort to stop the shocks. At one point, as he was climbing down a makeshift ladder constructed from a floor truss, he shifted the power saw from his right hand to his left hand and was shocked. He fell from the ladder into a puddle of water, still hold- ing the saw. The current had caused his hand to contract, and he was “locked” to the saw. A co-worker disconnected the power cord to the saw. CPR was given, but the shock was fatal. Attention to these general safety principles could have prevented this death. • Any and all electrical equipment involved in a malfunction should be taken out of service immediately. The carpenter should have taken the saw out of service, not just the extension cord. (As it turns out, the saw was the source of the shocks, not the cord.) • Although the homemade extension cord does not seem to have contributed to this incident, it should not have been used. • The floor truss should not have been used as a ladder. For climbing, use only approved ladders or other equipment designed specifically for climbing. • Do not work in wet areas. The water should have been removed from the floor as soon as it was found. Humidity and perspiration can also be hazards. Try to stay as dry as possible, be alert, and take action to protect yourself when needed. • OSHA requires that all receptacles at construction sites that are not part of the permanent wiring have GFCI’s. • Be aware that shocks can cause you to lose your balance and fall, often resulting in more severe injury. wire. Power tools with metal housings or only one layer of effective insulation must have a third ground wire and three-prong plug. u Use multiple safe practices—Remember: A circuit may not be wired correctly. Wires may contact other “hot” circuits. Someone„ Wear and maintain PPE. else may do something to place you in danger. Take all possible precautions. Wear correct PPE OSHA requires that you be provided with personal protective equip- ment. This equipment must meet OSHA requirements and be appro- priate for the parts of the body that need protection and the work performed. There are many types of PPE: rubber gloves, insulating shoes and boots, face shields, safety glasses, hard hats, etc. Even if laws did not exist requiring the use of PPE, there would still be every reason to use this equipment. PPE helps keep you safe. It is the last line of defense between you and the hazard.Page 66 Section 8
  • 74. H A Z A R D S : S A F E WO R K P R AC T I C E S u Wear safety glasses—Wear safety glasses to avoid eye injury. Wear safety glasses to avoid eye injury. u Wear proper clothing—Wear clothing that is neither floppy nor too tight. Loose clothing will catch on corners and rough sur- faces. Clothing that binds is uncomfortable and distracting. u Contain and secure loose hair—Wear your hair in such a way that it does not interfere with your work or safety. u Wear proper foot protection—Wear shoes or boots that have been approved for electrical work. (Tennis shoes will not protect you from electrical hazards.) If there are non-electrical hazards present (nails on the floor, heavy objects, etc.), use footwear that is approved to protect against these hazards as well. u Wear a hard hat—Wear a hard hat to protect your head from bumps and falling objects. Hard hats must be worn with the bill forward Arcing electrical burns through the victim’s to protect you properly. shoe and around the u Wear hearing protectors—Wear rubber sole. hearing protectors in noisy areas to prevent hearing loss. „ Think about what you are doing. u Follow directions—Follow the manufacturer’s directions for clean- „ PPE is only effective when used ing and maintaining PPE. correctly. u Make an effort—Search out and use any and all equipment that will protect you from shocks and other injuries. Don’t wear hard hats backwards! Section 8 Page 67
  • 75. PPE Fact Sheet—The Right Equipment—Head to PPE is the last line of defense against workplace hazards. OSHA defines PPE as "equipment for the eyes, face, head, and extremities, protective clothing, respiratory devices, protective shields and barriers." Many OSHA regulations state that PPE must meet criteria set by the American National Standards Institute (ANSI).Head Protection How do I wear and care for myOSHA requires that head protection hard hat?(hard hats) be worn if there is a risk of HEAD PROTECTION Always wear your hat with the bill forward. (Hatshead injury from electrical burns or falling/flying are tested in this position.) If you wear a hat differ-objects. ently, you may not be fully protected. The hat should fit snugly without being too tight. You shouldAren’t all hard hats the same? clean and inspect your hard hat regularly according to the man-No. You must wear the right hat for the job. All hard ufacturer’s instructions. Checkhats approved for electrical work made since 1997 the hat for cracks, dents, frayedare marked "Class E." Hard hats made before 1997 straps, and dulling of theare marked "Class B." These markings will be on a finish. These conditions canlabel inside the helmet or stamped into the helmet reduce protection. Use onlyitself. Newer hats may also be marked "Type 1" or mild soap and water for clean-"Type 2." Type 1 hard hats protect you from impacts ing. Heavy-duty cleaners andon the top of your head. Type 2 hard hats protect other chemicals can damageyou from impacts on the top and sides of your head. the hat. Don’t wear another hat under your hard hat!Class E, Type 1 hard hat. Class B hard hat.Page 68 Section 8
  • 76. Toe Do not "store" anything (gloves, wallet, etc.) in the helmet) and keep it out of direct sunlight. If you top of your hard hat while you are wearing it. The want to express your personality, hard hats come in space between the inside harness and the top of the many colors and can be imprinted with custom hard hat must remain open to protect you. Do not designs by the manufacturer. Some hats are avail- put stickers on your hat (the glue can weaken the able in a cowboy hat design or with sports logos. Never “store” anything in the top Class B hard hat in a cowboy of your hard hat while you are hat design. wearing it. Keep your hard hat out of direct sunlight when you are not wearing it! Use your head and protect your head! Section 8 Page 69
  • 77. S A F E T Y M O D E L S TA G E 3 — C O N T R O L L I N G PPE Fact Sheet (continued) Foot Protection approval stamp alone does not neces- sarily mean the footwear offers protec- Workers must wear protective footwear tion from electrical hazards.) Note that when there is a risk of foot injury from footwear made of leather must be kept sharp items or falling/rolling objects— dry to protect you from electrical haz- or when electrical hazards are present. As ards, even if it is marked "EH." with hard hats, always follow the manufac- FOOT PROTECTION turer’s instructions for cleaning and mainte- nance of footwear. Remember that cuts, holes, worn What about non-electrical soles, and other damage can reduce protection. hazards? How do I choose the All ANSI approved footwear has a protective toe and offers impact and compression protection. But right footwear? the type and amount of protection is not always the The footwear must be ANSI approved. ANSI same. Different footwear protects you in different approval codes are usually printed inside the tongue ways. Check the product’s labeling or consult the of the boot or shoe. Footwear will be marked "EH" manufacturer to make sure the footwear will if it is approved for electrical work. (The ANSI protect you from the hazards you face. Don’t take risks because you are wearing PPE. PPE is the last line of defense against injury!ANSI Z41 = ANSI footwear C = Compression ratingprotection standard [This code is more complex thanPT = Protective Toe section the others. Here is how to read it: of the standard 30 = 1,000 pounds;91 = year of the standard 50 = 1,750; (in this example 1991) 75 = 2,500 (in this example)]M = Male footwear(F = Female footwear)I = Impact rating(75 foot pounds inthis example—canalso be 30 or 50) MT = Metatarsal (top of the foot) protection rating (75 foot pounds in this example—can also be 30 or 50) Page 70 Section 8
  • 78. H A Z A R D S : S A F E WO R K P R AC T I C E S Summary of Section 8 Control hazards through safe work practices. Plan your work and plan for safety. Avoid wet working conditions and other dangers. Avoid overhead powerlines. Use proper wiring and connectors. Use and maintain tools properly. Wear correct PPE. Section 8 Page 71
  • 79. Glossary of Terms ampacity maximum amount of current a wire can carry safely without over- heating amperage strength of an electrical current, measured in amperes ampere (amp) unit used to measure current arc-blast explosive release of molten material from equipment caused by high-amperage arcs arcing luminous electrical discharge (bright, electrical sparking) through the air that occurs when high voltages exist across a gap between conductors AWG American Wire Gauge—measure of wire size bonding joining electrical parts to assure a conductive path bonding jumper conductor used to connect parts to be bonded circuit complete path for the flow of current circuit breaker overcurrent protection device that automatically shuts off the current in a circuit if an overload occurs conductor material in which an electrical current moves easily CPR cardiopulmonary resuscitation—emergency procedure that involves giving artificial breathing and heart massage to someone who is not breathing or does not have a pulse (requires special training) current movement of electrical charge de-energize shutting off the energy sources to circuits and equipment and depleting any stored energy double-insulated equipment with two insulation barriers and no exposed metal parts energized (live, “hot”) similar terms meaning that a voltage is present that can cause a current, so there is a possibility of getting shocked fault current any current that is not in its intended pathPage 72
  • 80. Glossary of Terms (continued)fixed wiringpermanent wiring installed in homes and other buildingsflexible wiringcables with insulated and stranded wire that bends easilyfuseovercurrent protection device that has an internal part that melts andshuts off the current in a circuit if there is an overloadGFCIground fault circuit interrupter—a device that detects currentleakage from a circuit to ground and shuts the current offgroundphysical electrical connection to the earthground faultloss of current from a circuit to a ground connectionground potentialvoltage a grounded part should have; 0 volts relative to groundguardingcovering or barrier that separates you from live electrical partsinsulationmaterial that does not conduct electricity easilyleakage currentcurrent that does not return through the intended path, but instead"leaks" to groundlock-outapplying a physical lock to the energy sources of circuits and equip-ment after they have been shut off and de-energizedmilliampere (milliamp or mA)1/1,000 of an ampereNECNational Electrical Code—comprehensive listing of practices to pro-tect workers and equipment from electrical hazards such as fire andelectrocutionneutralat ground potential (0 volts) because of a connection to groundohmunit of measurement for electrical resistanceOSHAOccupational Safety and Health Administration—Federal agency inthe U.S. Department of Labor that establishes and enforces work-place safety and health regulations Page 73
  • 81. Glossary of Terms (continued) overcurrent protection device device that prevents too much current in a circuit overload too much current in a circuit power amount of energy used each second, measured in watts PPE personal protective equipment (eye protection, hard hat, special clothing, etc.) qualified person someone who has received mandated training on the hazards and on the construction and operation of equipment involved in a task resistance material’s ability to decrease or stop electrical current risk chance that injury or death will occur shocking current electrical current that passes through a part of the body short low-resistance path between a live wire and the ground, or between wires at different voltages (called a fault if the current is unintended) tag-out applying a tag that alerts workers that circuits and equipment have been locked out trip automatic opening (turning off) of a circuit by a GFCI or circuit breaker voltage measure of electrical force wire gauge wire size or diameter (technically, the cross-sectional area) Endnotes 1. Castillo DN [1995]. NIOSH alert: preventing death and injuries of adolescent workers. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 95-125. 2. Lee RL [1973]. Electrical safety in industrial plants. Am Soc Safety Eng J 18(9):36-42. 3. DOL [1997]. Controlling electrical hazards. Washington, DC: U.S. Department of Labor, Occupational Safety and Health Administration.Page 74
  • 82. AppendixOSHA StandardsOSHA occupational safety and health standards for General OSHA standards related to electrical safety for Construction areIndustry are located in the Code of Federal Regulations (CFR), listed below:Title 29, Part 1910 (abbreviated as 29 CFR 1910). Standardsfor Construction are located in Part 1926 (abbreviated as 29 Subpart K—ElectricalCFR 1926). The full text of these standards is available on GENERALOSHAs Web site: www.osha.gov. 1926.400 – IntroductionOSHA standards related to electrical safety for General INSTALLATION SAFETY REQUIREMENTSIndustry are listed below: 1926.402 – ApplicabilitySubpart S—Electrical 1926.403 – General requirements 1926.404 – Wiring design and protectionGENERAL 1926.405 – Wiring methods, components, and equipment for1910.301 - Introduction general use 1926.406 – Specific purpose equipment and installationsDESIGN SAFETY STANDARDS FOR ELECTRICAL SYSTEMS 1926.407 – Hazardous (classified) locations1910.302 – Electric utilization systems 1926.408 – Special systems1910.303 – General requirements SAFETY-RELATED WORK PRACTICES1910.304 – Wiring design and protection1910.305 – Wiring methods, components, and equipment for 1926.416 – General requirements general use 1926.417 – Lock-out and tagging circuits1910.306 – Specific purpose equipment and installations SAFETY-RELATED MAINTENANCE AND ENVIRONMENTAL1910.307 – Hazardous (classified) locations1910.308 – Special systems CONSIDERATIONS 1926.431 – Maintenance of equipmentSAFETY-RELATED WORK PRACTICES 1926.432 – Environmental deterioration of equipment1910.331 – Scope1910.332 – Training SAFETY REQUIREMENTS FOR SPECIAL EQUIPMENT1910.333 – Selection and use of work practices 1926.441 – Batteries and battery charging1910.334 – Use of equipment1910.335 – Safeguards for personnel protection DEFINITIONS 1926.449 – Definitions applicable to this subpartSubpart J—General Environment Controls1910.147 – The control of hazardous energy (lock-out/tag-out) Subpart V—Power Transmission and1910.147 – Appendix A—Typical minimal lock-out Distribution procedures 1926.950 – General requirements 1926.951 – Tools and protective equipmentSubpart R—Special Industries 1926.952 – Mechanical equipment1910.268 – Telecommunications 1926.953 – Material handling1910.269 – Electric power generation, transmission, and dis- 1926.954 – Grounding for protection of employees tribution 1926.955 – Overhead lines 1926.956 – Underground lines 1926.957 – Construction in energized substations 1926.958 – External load helicopters 1926.959 – Linemans body belts, safety straps, and lanyards 1926.960 – Definitions applicable to this subpart Page 75
  • 83. INDEXA D Galuminum wire hazard 24 de-energizing circuits 55 GFCIamp 6 (see ground fault circuit interrupter)ampacity 24 E ground 2ampere 6 electrical hazards, ground connection 47arc-blast 12 aluminum wire 24 ground fault 28arc-fault circuit breaker 46 damaged hand tool 31, 34 ground fault circuit interrupterarcing 12, 29 damaged tool 29 28, 34, 48, 61arthritis 30 defective insulation 26 ground potential 27AWG 39 exposed electrical parts 24 grounding 27, 28, 46 improper grounding 27 grounding path 47 guarding 43B inadequate wiring 24bonding 49 overhead powerline 25 overload 28bonding jumper 50 wet conditions 29 Hburns, arc 12, 15 hard hat 68burns, electrical 6, 10, 12, 15 electrical shock, amount 6, 11 hazards (also see electrical hazards),burns, thermal contact 12, 15 chemical 30 current density 9 duration 6, 7, 11 control (see controlling hazards)C path 8, 9, 10, 11 falling objects 32cable, 240v 4 receiving 2 falls 32cardiopulmonary resuscitation 17 electrical shock—what to do for 16 inadequate wiring 24carpal tunnel syndrome 31 electrocution, deaths 1, 7, 10 lifting 32circuit 2 energized 2 overhead work 30circuit breaker 29, 34, 50 evaluating hazards 19, 21, 34 particles 32circuit breaker, and leakage current 28 evaluating risk 34 hazardous environments 51clearance distance 26 extension cord 24, 34, 42, 46, 63clues of electrical hazards 34clues, I blown fuses 34 F impedance 8 tripped circuit breakers 34 falls 56 insulation 26, 44 tripped GFCI 35 fault 27 insulation damage 45 warm extension cord 34 fault, low current 47 isolation 43 warm junction box 35 fire extinguisher, types 14 warm tools and wire 34 fires, electrical 14, 24, 28, 29 worn insulation 35 fires—what to do 14 JCode of Federal Regulations 75 fixed wiring 40 jewelry 56concussion 12 flexible wiring 41 jumper, bonding 49conductor 3 foot protection 70controlling hazards 19, 21, 36, 54 freezing 6CPR (see cardiopulmonary fuse 29, 34, 51 K resuscitation) kill switches 17CFR (see Code of Federal Regulations)current, L calculating 42 ladder safety 58 current 2 leakage current 28 effects on body 7 live 2 path through body 8, 9, 10 lock-out/tag-out 37, 38current leakage 47 lock-out/tag-out checklist 38cuts 31 low back pain 31Page 76
  • 84. INDEXM P TmA 6 personal protective equipment tendinitis 30milliamp 6 31, 66, 68, 80 tools 64milliampere 6 perspiration 30 tools, double-insulated 65 plugs, three-prong 62N power 42 VNational Electrical Code 15 power rating 42 PPE ventricular fibrillation 6National Electrical Safety Code 19 (see personal protective equipment) voltage,NEC (see National Electrical Code) high 7, 12NEMA 63 low 6NESC (see National Electrical R voltage 2 Safety Code recognizing hazards 18, 21, 22nonconductive material 28 resistance 8 resistance, effect on current 8 respiratory paralysis 6O risk 34Occupational Safety and Health risk evaluation 34 WAdministration 15 wet conditions 29, 61ohm 8 wire gauge 24OSHA (see Occupational Safety and S wire size 24 Health Administration) safe work environment 19, 36overhead power lines 25, 61 safe work practices 19, 54overload 28 safety model, overview 18 shock (see electrical shock) shocking current 6 short 34 Photo and Graphics Credits ©P. Barber/CMSP—9 Karen K. Miles—14bc, 18, 19, 23b, 24, 25b, 37b, 39, 48, 58c, 61, 62, 64a, 69b Richard Carlson—23a, 26b, 57, 65a ©PhotoDisc—1, 2, 3, 8, 14a, 28ab, 29, 32b, 40, ©Corbis Images—6 43a, 44, 46b, 47b, 58a, 59bc, 66 ©M. English/CMSP—10 ©PhotoQuest—25c, 43b Thaddeus W. Fowler—34, 46a, 47a, 51 R.K.Wright, M.D.—www.emedicine.com Cat Goldberg—cover, 5, 20, 25a, 26a, 27, 30, 31, 12, 67b 32a, 37a, 38ab, 43c, 49, 50, 55, 56, 58b, 59a, 64b, 65b, 67ac, 68abc, 69ac, 70 Page 77
  • 85. To receive information about occupational safety and health problems, call NIOSH at 1-800-35-NIOSH (1-800-356-4674) Fax number: (513) 533-8573 E-mail: pubstaft@cdc.gov or visit the NIOSH Web site at www.cdc.gov/niosh DHHS (NIOSH) Publication No. 2002-123 Delivering on the Nation’s promise: Safety and health at work for all people through research and prevention